sounds like:
(German) Peel No 24 Patrick St RENNIE Robert Head M M 67 Mariner --- born Ireland
(German) Peel No 24 Patrick St RENNIE Agnes Wife M F 65 ((Mariner Wife)) --- Ireland

there is one other rennie on island in 1881
Lonan 7 Baldooin Road Alma Terrace HENRY William Head M M 62 Lead Miner --- born IoM
Lonan 7 Baldooin Road Alma Terrace HENRY Jane Wife - F 60 --- --- IoM
Lonan 7 Baldooin Road Alma Terrace HENRY Hannah Daur U F 27 Milliner --- IoM
Lonan 7 Baldooin Road Alma Terrace HENRY Eliza Mary Daur U F 20 Dressmaker --- IoM
Lonan 7 Baldooin Road Alma Terrace RENNIE Ann Jane Daur W F 31 Independant Means --- IoM

the name doesnt occur in my pages except for Sir John Rennie who did the breakwater in Douglas