And how old are the grandkids - cause roosters and small children are not a great combination. Roosters often attack children before they attack adults, so it seems to come out of no where.
I am going to give the advice you don't want, but feel honor bound to throw it out there. If you don't want it, that is fine, they are your chickens.
One does best with the least amount of roosters for the needs of the flock. I would not want 2 roosters with less than 15-20 birds. Even then it is tricky and often times does not work. They don't call it cock fighting for nothing.
The idea of adding hens to bring up the numbers sounds good, but unless you are buying full grown hens, you are months and months away from that being a solution. That is a long time for either your single hen to take the attentions of two cockerels, or a long time to live alone if you separate her.
Cockerels tend to be darling, we have all been there, they are inquisitive, brave, approach us like they like us. That is a misinterpretation. They approach because they have little fear, and often times that leads to aggression to people. Yours are in the darling stage now, but it often does not last.
Also know, that todays behavior is no indication on tomorrow or next week, or next month. Being raised together has almost no influence on future behavior.
At the least - set thing up so that they are ready to go, so that you can either separate fighting cocks, or pull the pullet away from constant harassment.
I would strongly suggest letting both boys go, look around locally and seeing if you can get a pair of hen. An all hen flock is a nice way to start. Then next year, with a little more experience, you can add some more, and if you get a rooster, see how it goes.
Just because you accidentally got cockerels, is not a reason to keep them.
Mrs K