Ovulation can potentially happen anytime in your cycle. Having sex twice monthly may miss that period. The success rates depend on the reason of the insemination. In general, your pregnancy is improved with AI, but the actual number depends really on why it's being done, how old the mother is, etc. I have read that ovulation takes place twice.
Most women ovulate only once a month.
Sometimes, a woman can eject two eggs, that's how twins sometimes happen. I have tried IVF twice, and both failed since I had only two eggs to harvest that time. I have severe endometriosis. Many doctors think that implanting three fertilized eggs may improve pregnancy outcome, so they do not do IVF unless there are at least three good eggs. My last-born child was born with a hearing loss from what they called rubella syndrome.