“Can it even be done” is a good question. Another thing that gets debated a lot is, is a person admitting some sort of guilt by accepting a pardon? Like, it’s not an official admittance of guilt, but since a pardon is forgiveness for a crime/offense, it does carry the implication that the person that has accepted a pardon committed some sort of offense against the US.
Sweeping pardons that include a crime but go beyond it, like Biden’s pardon of Hunter have been done before, but this is different. I am kind of doubtful that it can be done but I imagine our friends at the SCOTUS could be involved at some point.
I think maybe it would depend on how the pardons are worded maybe. The Constitution doesn’t say there has to be a charged crime, but there does have to be an “offense against the United States,” in order to pardon it. I wonder what offenses Biden would list?
I’ll add this whole thing to the list of Constitutional crises that Trump has created over the past 8 years, of which there have been several.
EDIT: I forgot to answer your question as to why Biden would do this. Because Trump has threatened these people without any basis and now has the power and the immunity to make good on those threats. Biden I think would be trying to protect them through whatever means he feels he can.