Cat Peeing Outside Litter Box?

I have a female cat, almost 2 years old, named Lady Kitty. She is fixed, however my boyfriend and I got two brother kittens who are now 6 months old and are not fixed.

Lady Kitty poops in the litter box shared with the two male cats, but refuses to pee in it. She will pee in a very small cramped space between the toilet and the cabinet thingy, she also pees right outside in front of the litter box, and on the side of the litter box. The litter box has a top on it if that's a big deal in the problem.

I know she's not acting out to be mean because she's a very nice loving cat. She's a little skiddish, but that's only after she pees outside the litter box. She loves the kittens, she cuddles with them all day and cleans them. I don't know if the enclosed litter box is the problem, the kittens not being fixed, or that I need more litter boxes. I don't know what else it could be. I do know my boyfriend won't let me keep her if she doesn't stop peeing outside the litter box. She's a good girl and I love her. Please anyone that studies cat behaviors or someone that can just help me solve this problem please either get ahold of me or comment a solution. I'm in desperate need of help for this issue. Thank you.

By Alli Marie B. from Oneonta, NY