My pair of male cockatiels used to do this. They died 3 years ago. I don't know how, but it was from natural cause. The younger one died 9 months after the older one died. R.I.P I love and miss them so much.
Genetically it's better to pair Papao with Pipo because they both are ring eyed lovebirds, although one is a personatus one is a fischer. Pippin is a roseicollis, non ring eyed species... although I don't mind having kids from this couple. It's just that non of the females will successfully mate with Pipo. 1 has weak knees, the other one is simply smaller than the male.
Yeah, in fact I've seen Pipo tried to mate with them both but those girls can't squat stably with Pipo on their backs. It'll be best if the female is bigger than the male, and has normal strong legs, like Pico-pence couple.