"Premptive pardons" are not pardons at all, but grants of immunity. The Constitution provides no such power to the President. Plainly Trump's DOJ needs to find a solid case against one of those granted one of these "pardons" and bring an indictment so that the SCOTUS can rule them invalid. We have originalist judges in the majority, and none of the Founders would recongize these as pardons. Personally, I favor finding an indictable case against Fauci, simply because his misconduct in allowing the funding of gain-of-function research to be funded overseas killed millions, and was not a personal attack on Trump, so that prosecuting him cannot be portrayed as venial "revenge".
Of course, if the SCOTUS for some reason rules them valid, then every one of the beneficiaries should be dragged in front of every relevant Congressional committee and forced to testify about whatever it was that made Biden think they might be targetted, with referrals for contempt of Congress forthcoming and pursued by the DOJ if they don't (cf. the treatment of Steve Bannon).