Most of the Gasters actually had pretty decent relationships with Asgore and Toriel, and are even considered close friends to a certain point.
Victor (Underfell) and Pluto (Swapfell) were even considered confidants to Asgore after Toriel left. Don (Mobtale) was also considered this before his betrayal to the "crown."
Asgore, after his children died and Toriel left, also kind of saw Gaster as a sort of son, so also had a tendency to be a bit nosy about certain things. Wing (Undertale), Teddy (Horrortale), Stars (Outertale), Waltz (Dancetale), and Echo (Swaptale) didn't mind as much. They liked to ramble and Asgore liked to listen. Victor (Underfell), Pluto (Swapfell), Ivory (Underlust), and Don (Mobtale) didn't like it so much, however. For their own reasons.
I want to talk about Gaster and Mc's relationships in Babybones. Soooo, I'm gonna do that. Can be taken as general too, what they're like in romantic relationships.
Wings (Undertale Gaster) and Momma have a... good relationship. Wings has a bad habit of making Momma have a heart attack and keeping secrets from her that he shouldn't (like Sans and Papyrus' creation). He really loves her though, listens to her and very affectionate. She does the same for him. She also helps him with outside interactions and reigns him in, since he can be kind of oblivious to other people in his scientific pursuits.
Echo (Underswap Gaster) and Momma have a bit of a strained relationship. Echo is very focused on his work and tends to forget entirely about her and his family. He never told Momma about Sans and Papyrus' creation and she didn't find out until she came to the lab to drag Echo home. It's not malicious, he's just very ditzy and spacey. He just... forgets. Momma recognizes this and tries to help, even if she gets tired of it a lot. The kids were a big fight though, she was not happy she had to find out about them herself.
Victor (Underfell Gaster) and Momma actually don't have that bad of a relationship. Victor is very attentive and affection with Momma, but that's mostly do to his obsession with her. The beginning of their relationship wasn't... great. Momma didn't have much of a choice in the matter, but he made it seem like the obvious choice. No one would mess with her with his claim on her. Despite this, he's not a bad husband at all.
Pluto (Swapfell Gaster) and Momma have a very unhealthy relationship. It's kind of a debate on whether they even like each other or not. Pluto did charm Momma in the beginning, but... it was mainly a front to get her to agree. He needed a wife, due to Toriel's needling,, and he saw her as the best candidate. After he got what he wanted, he started ignoring her. But he won't let her go now that he has her either, even if she wanted to. It wouldn't be a stretch to say Momma's scared of him.
Teddy (Horrortale Gaster) and Momma had the same as Wings (Undertale Gaster) and Momma had. But if he ever escapes the void and reunites, he'd be a lot more affectionate with her, more focused and devoted to her. His loneliness in the void and having to just watch her and his kids suffer without being able to do anything about it really hit him. He'd be very focused on taking care of her afterwards.
Ivory (Underlust Gaster) and Momma, again, had the same relationship as Wing (Undertale Gaster) and Momma had. But after the experiment, Ivory got a lot more hands on. As in, they could barely keep their hands off each other for more than a minute. It could be said he's a bit obsessed with her, but she'd be just as obsessed with him in that case. They love each other very much, even if Sans and Papyrus would prefer not to see it so much.
Don (Mobtale Gaster) and Momma have a bit of a strained relationship. They love each other, a whole lot. Don charmed Momma and she happily married him. But... he wasn't all he seemed though. He's controlling and shady, mainly due to his desire to keep his family safe. But it makes her a pretty bird in a cage. Always having him or some type of protection following her whenever she went anywhere alone. It tipped her off that something was off, and with the inclusion of her kids, it gives her a lot of anxiety.
Stars (Outertale Gaster) and Momma have a very happy relationship. They're a very loving couple. Momma has to drag him away from work sometimes, but he always makes it up to her. It kind of endears her more to him in this case. They're a bit more attuned to each other too. It's clear to anyone that sees them that they've chosen each other, and that they adore the other. An old couple that still seems freshly in love.
Waltz (Dancetale Gaster) and Momma have a very similar relationship to Stars (Outertale Gaster) and Momma. Waltz and Momma are very attuned to each other, again an old couple that seem to fall in love all over again whenever they see each other. Waltz is focused on his work, but he's very quick to drop it the moment Momma calls him. He's very attentive towards her and her to him. They have a hard time looking away from each other, especially when dancing. And it's very clear to anyone watching them dance together that they fit together like puzzle pieces, two halves of a whole.
