Here is a thought: do you have any way to lease them? We are leasing our gelding that no one rides. It is an on site lease as we have an arena and some trails nearby. I don't know your facility, but that might be helpful in getting their care paid for and getting some miles on them to make them more suitable as 'kids horses' since most people buying older horses like them to be appropriate for children, unless they are broodmares, and then the arabian horse sites would be the best place to market them, especially if they have successful progeny or brothers/sisters. A little research into their siblings and offspring will help.
If not, it may help between now and when you plan on moving them to make a good effort to ride them quite often and get them more suitable for youth riders as that is really the market for an older horse.