"Are grandma and grandpa married?"
Translation:Ovatko mummo ja vaari naimisissa?
Both are common -- it all depends on the family. You might even use one for the maternal and the other for the paternal grandmother, to make the distinction. The same goes for vaari and ukki for grandfathers.
Mummo is also a more general word for (very) elderly lady, although whether it's a polite word to use for any old lady depends on the context.
The other ones (mummi, vaari, ukki) are not used as general words for old people, but specifically refer to family members.
Yep, and there are plenty of others as well. My dad's parents were always "pappa" and "mummi", while my mum's parents are "ukki" and "mummo".
You either use "mummo", "vaari" etc. as is or include their names, in which case they are written (and said) as e.g. "Maija-mummo".