How do you think breeding would work?

Impossible to say, since breeding isn't implemented.

If it's anything like the games, it won't guarantee you 100, but high IV ditto will be helpful.

Breeding from main games gets some IVs from each parent, then randomly selects the remaining IVs. If implemented like that, then maybe the child of two 100% would be guaranteed two IVs at 15 and the third randomly selected from 0-15. If breeding is ever implemented.

No way it works like dat. Maybe des best stat of each parent

According to this old picture of a gym I've found...