Maybe. They are living animals so there is no clear, sure answer of what they will do. It is very possible the rooster will bring them into his flock, but it is also possible the two will leave to try to find their old home. What I'd suggest is locking them in something for a week or so until they get used to being there. It is best if it is where they are locked is in the coop so they will want to go to bed there when they have the choice, but you can manage that issue later if you have to house them somewhere else.
I really like housing them in the coop where they can see each other. That helps integration. When you do let them mingle, they will have to settle pecking order issues. That might get violent or it might go extremely smoothly. There is no way to accurately predict what will actually happen. It is also possible the new hens will stay by themselves for a while, but eventually they should start hanging together.
Then you have the quarantine question. With as few chickens as you have and are bringing in, I personally would not worry about it unless the flock they are coming from looks unhealthy, in which case I would not bring them in anyway.
It is possible that the chickens could bring in a disease that can wipe out your existing three birds. If you hold the new chickens in isolation for a month, they might show signs of a disease. If you had a large flock, that is probably good idea. But it is also possible that either flock, the existing one or the ones you are bringing in, have a disease that they are immune to but can pass on to the other chickens. No matter how long you quarantine them, that disease will never show up. Quarantine is mainly checking to see if the new birds have been exposed to a new disease in the last several days. What I normally would recommend is to pick a sacrificial member of your existing flock and put it with the newcomers to check against this, but with your numbers, I'm not sure that is necessary.
You'll find that a whole lot of people bring home chickens from what are considered higher risk places, like chicken swaps, and seldom have an issue. If you do a formal risk analysis, the changes of something bad happening are pretty low, but if something bad happens it can be pretty bad, though most of the bad things that happen, like mites, lice, or worms are not that serious and can easily be treated.