cgh Never mind, I found it. Simon has to agree to support Esmeralda's desire to take control of the Unmen.
No, he doesn't. Esmera's deal (main deal) is about Unification Vote (second vote of Synod). If you make a deal with Esmera and then Simon propose "alternate form of unity" then Esmera's deal considered kept. Otherwise it's considered broken.
Sure, you can break the deal later, if you agree to support Esmera with Unmen and don't do it. But you don't actually obligated to support her here, since it's a new deal essentially. You are free to simply refuse her, it doesn't invalidate previous deal.
As for Kerannii, yes, it's quite possible to get the best results at Gawnfall with her, but it'll require some additional preparations. Well, that and you'd need to convince Yelarel to go for light reforms instead of moderate.