You don’t seem concerned that none of those people have been tried themselves but you presume they are guilty and disqualify them from constitutional duties.Even if they’re members of his party they don’t typically tend to be conspirators in the series of events that took place. How many Republican Senators in the Nixon trial were in on Watergate? How many people were in the room with Clinton during his deposition?
In this case there were more than a few members of Congress who helped the situation happen, and a few more who encouraged it.
Now, if you’re saying the Republican Party at large was responsible for the events then yes, maybe there is a problem with how the constitution sets out the proceedings.
None of the things you mention (evidence, witness examination, etc…) matter at all as long as the members of the jury are accomplices of the defendant in the crime he is standing trial for.
Mao would be proud.