Usually they would have to time it right and do it, A LOT, because betas aren't Alphas and their genes are "inferior". So, if they do get an omega pregnant it would be considered a miracle.
Seeing that he's a dominant omega, i think it's easy for him to get pregnant! But I'm not sure if he can get pregnant from a beta since they will have to "knot" them first ╮( ̄▽ ̄)╭
I can’t remember but can Betas impregnate Omegas in this ABO-verse? (I’m still sad that Heesoo and Dojun can’t have a baby )