Why rush the coming out party? It reads like you met them, they liked you and they came out.
I don't introduce my gf to my mother the second we meet. There is a growing period where people can see it working to build stability. This feels like everyone is so hopped up on being excited they are throwing it in the face of people that care about them.
There is a responsibility to being involved that can require some discretion. throwing alternate living in the face of the people that care most is a sure fire way to get up peoples protectiveness. Especially when kids are involved. Thats the most shocking thing. Its pure logic that this isn't going to fly in the face of the legal system.
This isn't a weak willed people situation... this is a people not realizing the reality of life.
Maybe next person you get involved with, you should (or they should since I am not sure where the pressure comes from) show some restraint and patience. This isn't a being open and honest thing. I am openly everything with my mother, but I am not going to throw my life in her face. Its just not polite. Introduce the situation slowly, show that it is stable and loving etc... maybe that will get you farther.