It all depends on how the hens treat the new tom.
Keep the tom separate where the hens can see him but not get to him. Once they get acquainted by seeing and talking but not touching, let him in with them while you observe. There will most likely be plenty of strutting by the tom and possibly by your dominant hen. There may be some dominance fights. At two, he is experienced and should take over pretty quick.
If there are dominance fights, the more you interfere, the longer it will take for them to work things out.
Good luck.