They'll be fine as a flock of 3, and they'll likely be fine if you add new additions. So it's really up to you and what you want, and the facilities they have. How big is your coop and your run? Integration is probably the trickiest part of the equation so if you don't have room to comfortably add more birds, I would say it's better not to even if you'd like more birds.
My first experience with chickens over two years ago only involved a small coop and the current run. At first, I had three hens and then added two more a few months later. I spent most of the day with them, making sure they were okay without separating them. Initially, there was a lot of bickering and bullying, but nothing too serious.
The coop's lack of windows made it dark inside, which worked in their favor as the new ones were difficult to attack due to poor visibility. The attached document shows my current set up. The coop is an 8x6 shed that was transformed into a coop and has two separate roosting areas. Under the primary roosting area, there are six nest boxes.
The 4x2 meter run is connected directly to the coop and has two distinct roosting spaces, as you can see. There are dust baths in the area, and I plan to add three more tires to create additional ones. I can cover the window to black it out when they're in the coop, since I can't separate them at night.
Assuming I proceed, I'll bring them back and present them to the coop, exhibit how to access it from the run, and use the plastic fencing seen in one of the photos to keep them separated during the day. Both groups will have an equal share of the garden, and both areas will have water, food, and shelter available. When it starts getting dark, I'll let them mix together while I'm around.
I'm leaning towards getting more and I have the advantage of being able to stay at home to monitor the situation and be alert to any issues.