when should both partners cum to have pregnancy

It doesn't actually work that way. You see, the guy has semen in his cum correct? You have an egg. The egg is already inside your body and inside one of the two tube-like things that lead to your ovaries. It's nice to cum but a woman doesn't need to do that as your body has everything in motion for you. All you need is for your man to cum inside you and hope that the semen reaches the egg. Try often or count days to figure out when you are most fertile.

Yeah, female orgasm is nice but not nessisary to concieve.