Male Dog MATED with other Male Dog

I am still shocked. My male dog actually mated with my other male dog. They are of diff breeds. They did not tie. I heard my smaller dog crying so I immediately went to see what was happening. The larger wouldn't want to get off the smaller one. I held the smaller then pushed the larger I think he was "done". I was so afraid that they'd tie coz that could really hurt the smaller one. good thing they didn't.

The smaller dog now has been wanting to poop. I guess because his anal sack opened. Should I bring him to the vet?

I have other female dogs in heat but they are in another part of the house, I don't want them to get pregnant. I understand dogs can smell the pheromones of those female dogs in heat. Could it be that this caused the urge and he just went it off with the smaller one?

I feel so bad for my baby :(