This might be doable in a basic form. I'm thinking that lords get something like 250 characters to write an oath for their estates, rather than per-estate. I (or someone) would need to look into how/where/if that text would fit into the estate selection screen.
An oath for all estates could be very handy for most cases but an oath per estate is even more intresting.
If i give knight a 35% and knight B 20%, perhaps i want more or something specific in return for the 15% extra.