Hi Lorraine.

Tom has:
Sarah Ellen GARRETT [aged] 54 yrs. [residence] Lifeboat House, Ramsey, [buried Maughold] 29 Mar 1928.

John GARRETT [aged] 59 [residence] Rhodesia Home, Stanley Mount, Ramsey, [buried Maughold] 11 Mar 1931.

Tom transcribed the parish register burials up until 1974 if you want any other entries.

I assume this is their marriage entry in Maughold?
12 Aug 1894
John GARRETT, Full age, Bachelor, Mariner, Ramsey, [father] Robert Garrett, Mariner
and
Sarah GELLING, Full age, Spinster, Ramsey, [father] Robert Gelling, Carter.

About the missing graves, as Frances suggested, the church should still hold the records of where people were buried, but would the exact place really matter? Now that you know they are all definitely buried in Maughold your mother might be happy just to see photos of the churchyard (I'm sure you would have taken some), and there are many more if you google it, including some very artistic ones including the ancient stones.

Also inside the church, e.g.
manxscenes.com/tag/maughold-church/

Sue