But they can be expelled from Congress.

Charging impeachment is a subjective call made by the House (the indictment). Trying is then done by the Senate (the trial). The closest thing they have to an objective definition is that the person be guilty of "high crimes or misdemeanors". Obviously a judgement call. So the answer to your question is, "Yes".

throughout this process would be tainted and accessories if they didn't speak up to the authorities during the collusion.

I think they could be pressured into resigning their jobs. Not sure of any legal implications - but I'm sure if Mueller proves any of this out he'd have the answers.

One couldn't trust any elected official going forward if they had knowledge of crimes being committed by the Trump team. They would have to be removed from office. I'm thinking forced into resigning.

Congress doesn't have the immunity given a President for crimes, so they can--and have been--indicted, tried, and convicted of crimes. A 2/3 majority can expel a felonious Congresscritter and/or Senator.