They're a poly, your honor
Just so y'all know what Ebony's relationship actually looks like (more info under the cut)
Muriel and Ebony live together, keep their adult lives running together, and do a lot of romantic stuff together. They would absolutely be including Nadia in that, but she has countess duties and lives a lavish life in a heccin big palace with lots of people, which just doesn't work for Ebony and Muriel. Since they can't really work past that, the trio have a... unique dynamic. They try to have regular romantic outings, usually in the evenings, and which often end up testing their individual comfort zones. Ebony visits the palace at least weekly, acting as advisor, confidant, whatever Naida needs. Muriel and Nadia are a lot more casual than that, but they're both big on physical affection.
Portia is Nadia's life partner, and while she doesn't help out with the countess stuff she is able to be there full time. Her interactions with Ebony and Muriel are primarily platonic, best-friend type stuff, with occasional hints of romance because why not. It's very common to find them all building pillow forts, gardening, baking, making cuddle piles, and other fun homey stuff like that. Nadia joins in when she pleases.
(also Muriel, Portia, and Nadia all Do the Do with each other, but Ebony and I are to ace for that so I am not filling in the gaps there)
