Can ecrubh learn to lunge with Bay? I don't think that lunging Cyn will cause you to bond too much with her over ercubh. Horses just know what they can get away with with one person over another, that's all. If he gets out there and does one on one things with her like grooming her and pampering her, she'll bond with him right quick :-)Grooming is a great bonding process.
I think feeding is good too... Learn who butters the bread. ;~D I try to have ecurbh feed her in the evening.