(Like most of my PolyPINC posts, this one is based on Linked In Life And Love, which is a really good Pollination AU by @l-omegainfinity-l that you can find here and should definitely check out)
I think Neo would tell Roman that she's dating all three of her teammates pretty soon after they got together. Roman would make some sort of snarky remark about Neo taking after her cousins, Neo responds that they each have two girlfriends and she has three so she's winning, Roman asks if they're treating her right (Neo nods) and if she's treating them right (Neo nods harder), and that's pretty much all he needs to know to be happy about it - and, after Neo and her girlfriends get a Mate's Mark, Roman gladly welcomes three more people into Remnant's Messiest Family
Pietro is the second of Team PINC's parents to find out - Penny introduces him to her teammates over a video call, then explains that her teammates are also her girlfriends. Pietro's surprised but also happy that Penny is with people who love her. A while later, Team PINC travels to Atlas and Penny introduces her girlfriends to her father in person; the three of them make a pretty good impression on him, which is great because by that point the PINCs already have their Mate's Mark and that kind of explanation goes a lot smoother if your dad already approves of your romantic partners
On the same visit to Atlas, Ciel meets up with her own parents and. Okay, we know basically nothing about Ciel's home life in canon, LiLaL describes Ciel as a "homeschooled prodigy", and my own headcanon for both versions is that Ciel comes from a military family. I'm not sure how they'd actually react to their daughter's three girlfriends, but Ciel would definitely be nervous about making that particular introduction - she really wants her parents to like her Mates - let alone explaining that their "matching tattoos" are actually the physical manifestation of an aura bond and the Faunus cultural equivalent to an engagement ring. The only reason she's able to go through with it is because her girls are sensing her lots of encouragement and positive feelings through the Link
At some point, one of them - maybe Penny? - asks Ilia when they'll get to meet her parents. The sudden wave of Sadness that comes off Ilia after that pretty much answers that question, so Penny, Neo, and Ciel immediately hug Ilia. The four of them sit like that for a while. Eventually - maybe a few hours into the group hug, maybe several days later - Ilia opens up to her girls about how her parents died
If that last one happens before the PINCs go to Atlas, maybe when they are in Atlas, they end up doing a mission clearing Grimm out of an abandoned Dust mine only to find out that it's that abandoned Dust mine...
