Its a good, story them not having a kid is fine for me. Not every omegaverse manga story i've read has those anyways and if there was a kid it wouldn't have a partner and the story would still end here.
Okay let's talk about me saying their kid wouldn't have a 'partner' its cause they we're the last omega and alpha parents. Unless the kid can be a beta (which is possible i think?).
Story is a good 9/10.
His sister only acted that way cause it worried her that he would have a hard time carrying a baby if he would carry one. And i understand that. Its the same as a younger sister worrying for her older sister and causing her older sister to have problems and such. So good story overall stop saying that you're sad cause there wasn't a kid.