As an example, my girls are also litter mates (as far as I know), and have been with me for 3.5 weeks. They definitely seem to be friends but they also dont really snuggle up together.
Patches is the dominant one. As a result, she gets first dibs on everything. When I put fresh hay in, she's first in and will chase Nia out if she tries to go in. Nia has to stand next to the hay box eating what she can from there, until Patches is finished, only then is she allowed in. Same with pellets - I put the bowl inside a hidey house. When I top it up they both come running. But patches goes in first and won't allow nia in until she's done. Same with veg - if nia takes something patches likes the look of she'll try take it out Nia's mouth. Nia puts up with it all fairly well. We had a lot of dominance displays the 2 days they were in season (first nia then 2 days later Patches), but generally nia accepts her position and goes with it. They often sleep and/hide together in their main hidey house, but they don't snuggle up to each other. But when I take patches out for lap time (she's by far the most confident), after a few min she starts calling for nia
Same with when I take nia out, a few min later Patches calls for her.
So you, they're not all snuggly together all the time etc, but they definitely get along and seem happy together. Patches just makes sure nia knows who's boss and nia seems fine with her position (except when she's in season then she tries to take over).
[Just a brief aside - I have watched carefully and although patches chases her out both the hay box and pellet house, she does still get her turn and get to eat fine, patches just insists on going first, but nia is free to go when patches is done]