I have two females who are not litter mates but were raised together from a young age. They are in a 4ft x 2ft cage with a layer of sawdust and the hay piled high enough to bury in. They also have a choobe and two boxes to hide in.
My problem is though, they keep scrapping. Not constantly but it's enough to worry Me. I don't want to split them unless I really have to.
Our three girls can be grumpy. We regularly have ear nipping, nose offs, butting each other out of the way and generally being a nuisance to one another. It looks much worse than it is-they really do love each other and pine for whichever one has had to go to the vet.
The key thing is whether or not they're having bloody fights. That's very difficult to overcome.
When my two (unrelated) sows come into season, they are little swine . They have lived with neutered boars (Gp3 then GP6) so I do expect them to go full throttle into mardiness and they don't disappoint
I find the telltale sign is their pee smells stronger.
You might find they will snipe at each other regularly, one will be Alpha. Do they have a run (4'x2' is the minimum size for 2 adults). They might enjoy a new scene with some new boxes and bags to play in? Gumtree has some bargains.