Based on Roderick's "If you’re an Usher, the gates are open. Period." line from episode 1.
I don't have the brain power rn to fully flesh it out. But the main idea is that the Usher siblings just lowkey invade each other's houses. Not so much "get out of my room" but like "bring some chips on the way over." The gates are open to family and family only.
Like Freddie is older than Tammy. Which means he probably moved out first. Tammy, still in high school, hanging out (taking refuge) in her brother's apartment to be away from their dad for a bit. They love the man, honestly, they do, but sometimes he's a bit much.
Vic, for now the baby sister, hopping between Freddie's place and Tammy's place when she's in some fancy university (assuming she met the family when she was like early 20s as its implied she was around for a bit before Leo, Camille, and Perry showed up) and sleeping on someone's couch during finals week because one of her siblings lived closer to campus.
Leo, for now the baby brother, spends a lot of time at Freddie's place because Freddie is eager to have a brother. (Not to say his sisters aren't great, but finally, there's another boy in the family.) Tammy's place is where he'll go to cook because she has the best kitchen to cook in and she doesnt mind it because he's not terrible. Vic, he goes to bother when the media hype around him is too much and he just wants to hide for a bit. (And she'll let him stay, she remembers what that was like.)
Camille, the baby sister and baby of the family for now, spends a lot of time at Leo's place. Leo's the closest one to her age and she feels safe with him. She's more intimidated by the older kids. But then she's over at Freddie's to occasionally hang out with her one year old niece (And Camille isnt the only one who babysits). She's going through Tammy's closet to borrow a white blazer cuz Tammy is the only sibling who dresses in muted tones most of the time. She's over at Vic's place watching shitty reality TV because Vic has the best TV at the time.
Then finally, Perry arrives. He's sixteen and he's almost a decade younger than his closest sibling age. But he's at Freddie's house and Freddie is teaching him to drive by doing circles in the driveway. He invades Tammy's house occasionally to steal her fruit because it just tastes better as does her tea, and Tammy's place is the best to pull an all nighter. He's casually breaking into Vic's place because he needs help with science homework and while the teachers could be bought, he really doesn't want to look stupid in front of the family like that. He'll be over at Leo's on the weekends playing video games with because Leo is normal and it keeps him grounded a bit. And then he's sometimes at Camille's because he doesn't know how to dress fancy and she's helping him pick out outfits for school events while coaching him how to campaign for things like Homecoming King and whatnot.
Like the Usher siblings who will invade Freddie's house for bowling. They invade Tammy's place to cook. Vic's place to do projects because she has a lot of space. Leo's apartment gets invaded for game night and Monopoly is banned. Camille is used to the sight of her siblings in her place because she has all those screens and horror movies with the siblings are always a delight. Perry doesn't get invaded as often as the others, youngest sibling perks, but if he is invaded by his siblings it's mostly just to see what he's up to and also because he's hungover after a night partying.
I am once again on the "it's a good thing they didn't love each other or it would hurt a lot more if they did, but imagine if they did" agenda.