How in the world do I deal with this?

So I had a potentially very ugly family issue dumped in my lap today. Here's a little background. I have an older sister with Lupus. But she also has another issue. A benign growth in her brain. It caused her to no longer be able to work as a software engineer. It literally made her IQ drop and she is very forgettful and gets disoriented driving sometimes, but otherwise she functions okay.
Of late she seems to be doing worse. She called our mother the other day to wish her and our stepfather happy anniversary but completely forgot that she spent much of that week in the hospital because my stepfather had major back surgery! That was odd. She also has made me uncomfortable of late and seems harder to get along with to me than normal.
The other day my Dad called me to find out how I was doing, but mostly to find out if I had heard from my older sister. I said no, I hadn't talked to her. He was a bit concerned because she doesn't return his phone calls. She and her husband get very busy sometimes--they run corporate bookfairs so I wasn't concerned.
That changed this morning. My mother called me. She is very upset. My sister is mad at her for some unknown reason. Won't return phone calls. Won't have anything to do with my mother (she got a short e-mail response saying she wants nothing to do with my mom) and that is worse because of my 3 year old niece who used to see Grandma all the time (the only grandchild and likely to remain that way). My older sister used to be so close to my mom she would call her multiple times a day.
Here's what I am afraid of. I know my older sister has some depression issues (one of the last phone calls my mom got was that my older sister was definitely unhappy and was talking about a divorce..something she has NEVER talked about before). I also know remember her complaining about her husband not doing this that or the other. He always told me that I wasn't hearing the other side of the story. It always confused me, because neither of them are liars.
However I now am beginning to believe that the growth in her brain may be causing her to become delusional. She may have imagined some fight with my mother (who is pretty easy going even if one of us is doing something she doesn't entirely approve of). It would explain why I keep hearing contradictory things.
This worries me greatly. My brother in law is not comfortable with Mental Health Issues. I think he believes its a personal problem not to be shared with others if at all possible. I worry that my sister might try to hurt herself. I worry about my niece. I worry about what my brother in law is doing. Short of showing up on the doorstep does anyone have any ideas how to handle this?
I have my own health and depression issues but I have long been considered the "responsible" member of the family and there was definite relief in my mothers voice when I told her that I would have my younger sister (who is closer to my older sis than I am) try to get in contact. However, I know this is going to be dropped in my lap because of my postion in the family and because I am geographically the closest to my older sister.
So, any ideas?

support as you can. Build some trust. If nothing else, it will help him deal with the situation better just knowing he's not alone. You don't even have to be direct about it. Just being friendly and checking in with him about other things more often at first -- it adds up.

I guess I'd do that first and see how that goes.

:hug: to you, turtlensue.

and my mom very much wants to do that. He has his own cell but I don't know if anybody has his phone number. I will speak with little sis tonight and see what she can do, but its a bad situation on top of my bad (but getting a little better) situation. Just remembering how upset my mother was this morning is stessing me out.
Thanks for the support. Talking this out helps for sure.:hi:

"handle it, Responsible One" mode and later realize -- hey, that was really stressful. (Good thing I didn't become an EMT or something, lol.)

Destress as you can, sweetie. Things will work out. :hug:

little sis talked to big sis and hubby on big sis cell phone. Husband did not even know my sister was mad at my mother. I am convinced my sister really heard my mother say something and heard it/processed it wrong. Says she is too mad to talk might e-mail her. I feel like I am seventh grade with this person said that to that person and the story keeps changing. Ugh.

and the rest of the family get that whole communication thing going. :hug:

I would encourage your brother-in-law to review these changes with her doctor. It might be depression, it might be medicines interacting, it might be the tumor, who knows? It needs to be checked out.

make sure all this is put on the table. it could be the tumor, or she may have some fibro with the lupus. it causes 'brain fog', and exhaustion that is depressive. you just get sick of everything, and want to crawl in a hole and be left alone. also, pain that you get f'ing sick and tired of.
if that is the case, there are treatments that can help.
at any rate, brains get sick like any other part of the body, and these sound like the symptoms.
let us know how it goes.

I just talked to my mother and tried to explain what my younger sister said. My mother says she has been crying EVERY SINGLE DAY because of this crap! I know my sister needs help but at this point I don't know that even if I could get a hold of her (questionable) I would be able to talk to her calmly and then she might twist my words all around (she actually did that to me the last time I saw her memorial day weekend). God help me if I suggest there is a mental issue. Although my younger sis did suggest counseling (marriage counseling) for her and her husband. What a mess. Its not helping my depression either to have to deal with this. I could TRY to stay out of the way, but thats hard too....I also keep hearing she thinks her health is okay....

man. ya know, i have been through a lot of this in my lifetime, and it is hard, hard, hard. i still have some scars. but do try to see, and help your mom to see, that what is happening is like a hallucination. your sister is seeing things and feeling thing, most likely, that are just outward manifestations of her brain being :shrug: poisoned, attacked, maladjusted, out of order. it is hurtful, but it is not really real. she needs help. you can't really see that your brain is hurting with a hurting brain. somebody has to help her. she is not likely to be able to see and help herself.
best of luck. give your mom a big hug from someone who has been there, done that.
:hug: :hug: :hug: :grouphug:

:hug:

She confirmed that the "conversation" my older sister supposedly had with my mother never happened, the phone cut off before my mom could respond to her "I want a divorce" comment. And despite talking to my younger sister the other day, theres been no other communication with my mom, not even an e-mail. Its now almost 2 months since my Mom has seen my niece. I am not even willing to try at this point even though I know she needs a lot of help. Even my Mother, as mad as she is right now, admits she is really worried that there is something really wrong with my sister. Yeah, is she is imagining conversations that never occured than that is a problem.....Really really don't know what to do...x(