I lost interest in swinging before I was ready to have kids so no advice on that front other than - most swingers I've encountered seem to take a break from the scene one they're actively trying to conceive and usually come back, if still interested, once done breastfeeding at the earliest but often not until kids were school aged with more options for childcare/ sleepovers while the parents were out. That's just the trend I noticed.
As for poly... hubby chose to walk away from a very young relationship when I got pregnant. Boy and I got MORE serious when I got pregnant. None of us dated while I was pregnant (minus one date that Boy went on but when I was home alone crying because I'd had a terrible day at work and didn't tell him until later because he was out, he felt terrible that he wasn't available and chose not to date again for a while). Little girl was probably a year or so old before anyone dated again.
Hubby and I are the parents, but Boy is very involved. He and little girl video chat when she hasn't seen him for a while. He is the go to childcare for my date nights with hubby. He disciplined and soothes and plays. He was there for part of my labor, barely missed the actual birth due to work.
Hubby's other partners at various times are NOT as involved. Lady, who he currently partnered to, has been around off and on as long as Boy has but not as consistently nor as often. Little girl is not comfortable with her at all, beyond general "I'll play with anyone mom and dad let me because I'm a kid and love attention" stuff. We do not try to hide our relationships, so she sees us cuddle and kiss people. She isn't traumatized yet.
It just depends on the relationships, though. Hubby and Boy get along great, and none of us believe in theoretical hierarchy (like hubby isn't primary while boyfriend is secondary - instead they're both my partners and get treated as fairly as possible while recognizing some scheduling priority and the like comes with sharing home, kid, finances).