First of all, introducing a new kitten into the household can take alot longer than 2 months. Especially when you have two older, established cats in the house. You're doing the right thing by keeping the kitten isolated in your room, only allowing her out when you can supervise. That's the proper way to introduce a new kitten. If you can get your hands on two baby gates, stack them one on top of the other in the doorway of your room. This will give them a chance to see and smell each other without hurting each other.

Define "attacking". If it's just hissing, growling and swatting with no bloodshed, that's normal. Another suggestion is to wipe down the kitten with a towel and allow the two established cats to smell her scent and vice versa, rub down the two older cats and allow the kitten to smell their scent. It's not going to happen overnight, but the love patience, treats and possibly catnip, harmony may happen.

Please give it a chance. And keep us posted.