There is history regarding alternative electors which dates back at least to 1960, when Hawaii did so. The practice is done to insure if a court reverses an election outcome , that the process of electing the President could continue without a hitch. Given that the states had pending lawsuits regarding the election outcome, there was nothing untoward selecting alternative electors.
In this instance, Nixon was VP and even though he was running against JFK, he rejected the alternative elector (a Republican elector) sent by Hawaii. Eventually, the election results showed that JFK had indeed won by 115 votes.
Pence followed a similar precedent. As no court had reversed the election results in the states in question on the day the electors were to vote (or subsequently), Pence rightly rejected the altternate slates of electors.
Pushing Pence to not certify electors is not illegal, any more than the pressure on Nixon had been in 1960. If Pence or Nixon had not certified electors sent and had instead moved to allow the alternative electors without a court reversing the elections in those states, then Pence not Trump would have to defend his actions in court.
Part of the issue with "charges" based on alternative electors is that given the on going court cases, it is entirely possible, though not probable that one or more cases could have overturned the election results in those states.
But at the end of the day, I think Trump owes Pence an apology. Because Pence played it "straight" the old adage "no harm, no foul" is likely to apply.
