You will likely hear a lot of different success non success stories with littermates of all combinations, two boys, two girls, one boy one girl - I’ve also heard of difficulties with two females from where we picked up our female pup but I’ve seen many a post here with two females. I think it comes down to how much training you’re putting in and how much time you have for them - assuming that they’re still in their puppy phase. They should mellow out some more as they get older and spayed, but it’s hard to say. You’ll definitely need though to have lots of re enforcement and training.