Two girl and boy cockatiel problem!?

Aww! Your male has a crush =3. BUT, I would tae the female out, get a smaller cage, put her in there, and set that cage next to the big cage. That way they can get used to eachother and h won't follow her around so much.

He's being a bit territorial. As long as you see no harm being done, by that I mean feather plucking and or bleeding, they should get along. A little squabbling is ok. I have birds that have been together for years and now and then will squabble. You should though introduce a new bird slowly at first. Set them cage by cage next to each other for a week or so. It's good for health reasons also. You never know what the new bird might be bringing with her.

You should have quarantined the new bird for 30 days in another room to avoid passing on any disease or infection to your other bird. Your male is just asserting his authority. Unless the new female is at least 18months old she shouldn't be in with a male. She would be too young to mate.

All males human and non human have to put on 'airs' telling the female/s that he is 'king' of his domain... some males will become physically abusive, some will become extra attentive, some will preen and display themselves or their gifts....

Once he is "convinced" she believes he is king of his domain and she is willing to accept him as a mate, he will start treating her less abusive. However, if she does not accept him as being king of his domain or considers him unworthy of being paired with... he will either continue his reign of terror, escalating in abusive manners or he will succumb to allowing her to be 'king/queen' of his domain and will begin acting like a plucked goose...

he is getting upset because a new bird is in his turf.

put the cages next to each other and let them get to know each other a lot slower.

best wishes!! :)