Congress impeaches with a simple majority. The Senate convicts/removes the impeached with 2/3 majority.
I think it would be doubtful to remove these senators through the House impeachment and Senate conviction/removal process. However, the scenario you described is plausible and disturbing.
They will face great pressure to resign and I’m not so sure the immunity from prosecution while in office will hold. If they decide to resign to cut their losses, the DOJ may still decline to prosecute knowing that that they’ll have to look at “everyone” and half the congress and the senate would be found to be guilty of something and would have to leave....which might not be a bad thing.