As I've always understood it, you capitalize monikers like mom,grandpa etc. when they can be replaced by actual names. 'Mom and Dad said' but not 'my mom and dad said'.
Mom and Dad can be replaced by Adam and Eve, but you can't say, my adam and eve'. My is a good sign to use lower case. You can't write ' my Mom and Dad' like you can't write, 'my Adam and Eve.'
I think sunandshadow said it right, when the title can be replaced by his/her name, capitalize. If not, don't. As soon as you write 'my', think lowercase.
'My grandparents'-lower case - 'Grandpa and Grandma said' should be capitalized.
(edited to add: 'his grandson' is the same type as 'my grandpa' - no caps.)
Last edited by elfin_odalisque : 01-29-2013 at 08:55 AM.