Do NOT offer to sell the domains to them - if they decide to be dicks and try to go the ICANN route that shows that you arent real interested in developing the domains and is one factor Icann uses in deciding cases
Of course unless they offer you a lot more bucks than you think you can make with them - of course you have to think down the road as to whether they might trademark the phrase - and they might have a small chance of getting them then - of course you could always trademark the name with your domain and then demand they turn over theirs
