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Dear LW,
Since you're weren't trying to evict your "friends", but the other way around, I don't see how you could be charged with discrimination. If your name is still on the lease I also don't see how they can force you to move. The question is, how much do you want to stay there?
I can't imagine that living with two hostile roommates and a newborn infant would be fun, but if you consider this place your home, you shouldn't be in any rush to move out. Perhaps you can tell the couple that you're sorry that it will be difficult for them to find a new place. Since they can't imagine having you as part of their new family, however, and it is your home, then they'll have to move. Give them a couple of months. If they refuse to do so, you could consider listening to loud heavy metal music at all hours or have lots of long dinner parties. You sound like you're too nice to take such tactics, but if the only other option is to move out of a place that you really love, then you have no choice. It won't be pleasant or easy, but neither is moving.
If you don't really care that much about the place or think you can find a new place easily, then move. But make sure to take everything last thing that belongs to you. You have already given the couple enough.