As others have said, do your children feel that they would like to come live with you if you should move to Dublin? It might be that the house you need is in a location which is not very convenient for them - intra-Dublin transportation links aren't fantastic in places.
Secondly you can fairly reliably predict how long they will be in college - if their ages are staggered as in most families, then the rent bill will start to drop as the oldest leaves college and (with every hope) get themselves a job where they pay their own way. Within a few years, you might find yourself with a big house and no children to put in it.
Thirdly and assuming that your mother would like to live independently for as long as she can, the point at which she needs to come to live with you is impossible to predict. Hopefully she (and all of us) will be sound in mind and body to always live independently.
It just seems a bit illogical to move away from the attractive lifestyle you have at the moment, at a time when the buying and selling houses is in a state of high uncertainty, without a pressing need. Strikes me as well that selling your (similar sounding) houses in the same town at the same time may reduce the potential to maximise sale prices. With fewer buyers around and less money to spend, might you find yourselves competing for what business is out there?
Has your mother indicated that she would like to move regardless of what you decide? She might find renting in Dublin to try it out first is a better option as it gives her a get-out clause in case she finds that its not what she thought it would be. She could also rent her own house out in the meantime to minimise the cost.