I don't think it's possible to be absolutely certain of what you would do before being in the situation.
My inclination however, is no, I wouldn't.
The main reasons being that:
a) not having an alibi doesn't make someone guilty. There must be other evidence that points to "guilt" that's invoking police interest
b) if I did do it and got caught the implications for the children of potentially having both parents incarcerated would be horrendous (even if the "crime" was to protect/avenge the children)
c) a good alibi needs more than just "because I said so". Even if it's "we were watching television together". It's all too easy to get tripped up by the most basic questions: "what programme?", "what did you think of that programme?". You'd have to meticulously plan every possible question/answer. If they were innocent the lying could make them look guilty.
d) I can't imagine DH ever requesting this of me. Based on the person I know, he'd never ask me to put myself in this position (same in reverse). If he did, it would be a big red flag tbh.
So as I said I can't assume exactly what I'd do, but point B would be a massive factor in making any decision.