Some Bantam roosters aren't willing to make too much effort to mate with hens if they already have easier hens. My experiences are with the breed of bantam cochins. My Bantam EE don't have that problem. Bantam cochins roosters seem to do better with 3-5 hens, and can be set in their ways. You...
Some Bantam roosters seem to just favor a hen or two. It's just easier for them. I'd give the new Frizzle some time. He has to earn the hens respect, and be confident to mate. Older roosters will often interfere with that.
How long were the pair's kept separately? I'd probably keep them...