Is that going to be enough hens to roosters to have them all get along?
How old are your current 1 boy and 2 girls? If they are old enough to act mature, are you having issues with that ratio? Many people don't. Some people have issues with 1 rooster and over 20 hens. To me the ratio of boys to girls is pretty unimportant. The actual personality of the individual chickens, boys and girls, counts for a lot more.
If you are worried about the boys fighting, they can fight to the death, they may fight some and reach an accommodation on how to manage the flock, or you might not see any serious fighting. Ratio doesn't matter, their personality does. If they are going to fight they will fight over 25 hens as quick as they will fight over 2.
4 EE hens and 8 BO hens? Also will they crossbreed? If so, how would I go about getting BO chicks?
I think you are planning on one flock of one BO rooster and 8 BO hens and a separate flock of 1 EE rooster and 4 EE hens. As long as you keep the two flocks separate the BO's eggs will give you BO chicks. But as others said, if the two flocks can mix they will not all be pure BO. They will crossbreed.
EE hens can lay white, brown, pink, blue, or green eggs. Them being called EE's does not tell you anything about what color of egg they will lay. I don't know why you want to keep the EE rooster. Purely your business. But if you get rid of the EE rooster and you can tell the difference in the EE and BO eggs, just keeping the BO rooster will assure the BO eggs will hatch out BO's. So don't incubate the EE eggs.
If you isolate the BO rooster and BO hens for a month (keep the BO hens away from the EE rooster) the eggs will hatch BO chicks.