A girl I dated years ago had three.

Also, I thought I saw an article a few months ago that was talking about science on the horizon about potentially no-mother babies in the future. So maybe we could eventually have two-mother or even multiple mothers.

And there's also polyamorous parents that co-raise kids. So if it's a closed polycule with like 5 people, one child could have, potentially, at least 5 moms, even today.

Obviously, we're talking about biological mothers vs emotional/practical/role mothers. But, even then, divorce exists. But if you want to just talk about bio moms, besides promising science (some that I didn't even mention), there's probably ways that some contextually specific intersex people could procreate, resulting in two biological mothers, even today. Or like one of those people who is two people genetically.

Basically, imagine harder.