All they need is doubt. Not even certainty. You have this rather a lot wrong. They have nothing at all to lose by making this choice.
Not every Republican state legislator is from a safe Republican district. Plenty of them have to win over swing voters. I also think you are underestimating the number of Republican voters who would have a problem with their state representatives voting to disregard the outcome of a Presidential election in their state absent compelling evidence.
Legally, they don't need any evidence at all to exercise their power to appoint electors. Politically, they'll probably need conclusive evidence.
And, wrong.
Politically, they need just enough evidence for doubt about the voting. And if you are really sure all those Republicans are from partly Dem districts, then they need just enough evidence to be able to sell it to the squishy.
In both cases, far far below what a court requires.
Andddd just looked at Wisconsin. Overwhelming majority Republican. You could let a few do a Collins and still send Trump Electors to the College, with total impunity.