I have kept Bettas with male guppies that have very small tails. Male guppies with huge fancy tails attract too much attention and are too slow to be able to avoid attack of a male Betta.
You would never be able to keep a Betta with guppies that you are trying to breed. They would eat the fry...
X 2 Bettas "can" live in a bowl, but they are not happy. Keeping a Betta in bowl with 2 cups of water is like putting a large dog in a crate and expecting him to be happy.