Hi Alan, I do not have any family in Yardley cemetery but generally I think when a grave is purchased all the details are put in a register and the purchaser is issued with the deeds. If the burial plot was a family grave - for more than one burial - the deeds are usually passed down the family as they have to be shown when the next person needs to be buried there. I am not sure if it is possible to get a copy of the actual deeds - I think only the next of kin would be able to do that as they prove ownership of the grave. But you should be able to find out the details that are in the register.
Probably the best thing to do is to contact the cemetery - you can email them on email@example.com or 0121 708 1831 or 0121 708 2183 and they might be able to tell you if they have the records there.
Happy Easter to you to Alan - I will try and be good and not eat too much chocolate