I have no connection to the Hughes' family. I am only helping. Do you have an address in Llandyfrydog for Richard & Mary Hughes ?
Llandyfrydog is a district near Llanerchymedd and Llanfair M.E and even like you suggested could be Dulas as the districts were altered.
I would like to help you but without dates/ ages it is difficult to find them.
There are Richard Hughes & Jane also Mary Hughes in the same grave at Llandyfrydog churchyard.
Please send more details,