Lovebirds fighting or breeding

Question
I have 3 young peach faced lovebirds in one cage. 2 of them are siblings and were bonded when I got them. Long story about how I got the 3rd. But now that the 3rd one's in there, he seems to be trying to mount one of the first 2 birds and she cries out when he's doing this. I can't really tell if he's mating her or biting her because he does it inside a bird hut. I understand that I need to take one of them out. But which one? I don't want the siblings to breed. So I'm inclined to leave the 3rd bird in with one of the siblings. Is he mating her or biting her? If he's mating her, he should stay with her. If he's biting her, I should remove her? Or should I remove him and let the siblings rebond? What a mess I have on my hands.

Answer
Hello Nina and thank you for your post.
Lovebirds are very aggressive birds, and the new one may be picking on one of the sibblings.
They all 3 need to be seperated.  Remember that lovebirds pick THEIR mates for life, and if they have not picked their mate, they will kill each other.
You can keep them in the same room, but just make sure that they are in different cages and do not let them out together.

Good luck and God Bless.
Dianna