That seems like the biggest question here. Forgive me if I missed that detail.

Beyond that, it’s really a mish-mash of details that need ironing out.
If mom insists on auntie watching the kids (for whatever reason) or if auntie insists, that’s good and well. Were I the father in this scenario, my stance would be simple: if you want to watch them, then that’s all good so long as homeboy doesn’t come around while they’re here. Otherwise, I’ll just find a different situation.

If dad is insisting on the kids going to auntie’s, for whatever reason, instead of another place, then he needs to find a new child care provider if he’s that uncomfortable with her man being around.