partner doesn’t ever want to tell their family that they’re poly

I’m 19f, my partner “Elliot” is 20nb, my meta “Katie” is 22nb. Elliot and Katie have been together for almost two years, and they’ve always been in an open relationship, but before Elliot started dating me, neither of them DATED other people, just hookups. Elliot and I have been together for ~6 months.

The problem is that Elliot has said multiple times that they don’t ever plan on telling their family that we’re in a relationship, or even that they and Katie are in an open relationship. They’ve said multiple times that I’ll be “a roommate forever” in the eyes of their parents. When I asked what their plan was for eventually telling their parents, they said “one day, my parents will die.” I’ve met their family, just as a friend. Their family knows about their relationship with Katie, and Katie’s family knows them as well.

This makes me sad. I don’t want to be some dirty secret from their parents forever. I get that it might not go over well to tell their parents, and it certainly wouldn’t have to be soon, our relationship is still very new. I just want to potentially eventually be viewed as an equal partner, and to me, not lying to their parents about me is a facet of that. It might be worth mentioning that my family knows about them and the poly aspect of our relationship, and has met both Katie and Elliot. It also might be worth mentioning that my mom is non-monogamous, and has been for my entire life.

I know I need to bring this up, but I don’t know how to do so without putting undue pressure on our relationship, or making myself look/feel selfish. I feel like asking would make them feel like I don’t understand how their parents are different from mine, and that they don’t have a good relationship with their parents— I do know that. I just also know that the idea of never being equally viewed as a partner makes me sad.