The only occasions I've seen George conversing with the mares (as opposed to yelling at them) have been when I'm holding one of them outside of the pasture fence, and George is on the inside.
George and the mare of the moment will then dare to touch noses over the gate. Usually squeals and strikes follow.
Today, I was inside the pasture, with Rose on a halter and rope to put her eye ointment on. George kept following us around. Finally it occurred to me that perhaps he'd like to say hello to her, that possibly the leadrope could function like an intervening gate, giving them both confidence to greet each other.
So I retreated to the far end of the rope and let George approach Rose. They touched noses. No squeals, no strikes. Then George curled his head around hers and opened his mouth playfully, but gently.
I think at that point, Rose decided she'd had enough, and after that she didn't consent to any further rapprochement. But that was a big step for both of them. George looked cheerful and inquisitive and not at all threatening. If he means to continue in this vein, I wonder how long it will take the mares to trust him.