If he appears twice it is because he was in the Kinsale fleet that left the day after the census and was counted twice, once in Peel and again onboard when the enumerators collected the forms probably in Kinsale. I'm not sure where the mariner's records were filed for 1891.

Marine Parade starts from the exit of Jib lane and ends at the cliff face - there were a couple of houses built on what is now the terraced bit of grass - 1864 valuation may help (the numbers refer to property in back green (Gib lane as well as Peveril Road)-
Green (ie Marine Parde as will be)
No. 9 house + yard owner Wm.Cashin occupier Edward Garrett value £5 - -

10 do do Robert Gorry- 2 - -

11
House & Garden
Esther Quayle
Danl.Kermode
3 10 -

12
House & Yard
Wm. Cashin
George Greggor
3 - -

13
Parcel of Land
Wm. Karran
Owner
7 6

14
House & Yard
John Cashin
Owner
3 - -

15
House & Yard
Susannah Cowell
Owner
5 - -

16
Half House
Thos.Cowin
John Cubbon
2 - -

17
do
Thos. Pickles
Jane Skelly
2 - -

18
House
do
Wm.Lace
4 - -

19
House
Margaret Coffee
Robt.Cubbon
2 5 -

Thus I think your missing houses as the small ones were demolished I think - later the numbers may have been changed