Grandparent names

My Mum wants to be known as Nanna. This is what I called her mother and I always assumed my children would call her Nanna. Since my LO has been born my MIL has decided she wants to be called Nanna too. I don’t want two Nannas, I don’t know how that would work! I would have preferred to let each grandparent choose their title but I really don’t want my MIL to be Nanna as well. I have started referring to her as Grandma. However, I don’t want to confuse our LO later on when she has a Grandma who refers to herself as Nanna! I asked DH about it and he had no problems with us teaching our LO to call her Grandma (his maternal grandmother is Grandma) and telling MIL that she is Grandma (or some other title of her choosing) not Nanna.

Has anyone else had experience with this?

Thanks!