I don't know much about breeding but I do know that there is a slim risk for infection during insemination and it might also be stressful for the female. If you don't do insemination and let them mate normally I'd be careful too as the female could possibly be sore from previous time and not even want to mate since she already did. I would personally go for the best suited male, the one that together with the female would better the breed, the one with the best hips, the one that has the best temperament, breathing and seems healthiest over all.
Me and my husband once went to a very respected Boerboel breeder here in South Africa, she explained how she chooses males for her females. Not always is the best male and female the best for bettering the breed, no dog is perfect, but she breeds to get the best out of both male and female regarding health, temperament and looks.
Breeding is such a big responsibility, it's your females health and sometimes life that's at stake. I would not use two different males, I've never heard of anyone who does and I spend quite a lot of time reading about it as I often times try to make people around me rethink when they say they want to breed their dog "just because". Here in South Africa we have a huge amount of unwanted dogs in rescues
I'm writing this with the best of intentions, I want things to go well for you and most of all for your bulldog and possible puppies