Hello and welcome

Firstly, there is a Mount Pleasant, Roscommon.
I see that Mary and son Frank give M P as birthplace in 1891 and Fanny/Frances shows Roscommon in 1911 indexes so it would seem that Roscommon is the place to look.
There is also a nephew Francis with the family in 1881, I think, so it might help if you could find a marriage record for him. Presumably, his father would be your Patrick's brother.
I have to say that I am not finding anything but hopefully these are hints for you.
I can't see any records for your names in Strokestown parish which is frustrating.
Here is Griffiths Valuation for Kilbride civil parish which includes Mount Pleasant.
http://www.failteromhat.com/griffiths/roscommon/kilbride.htmRegards
Heywood