Select the correctly punctuated sentence (both own the house):

A) My mother and father’s house is painted gray.
B) My mother’s and father house is painted gray.
C) My mother’s and father's house is painted gray.
D) My mother and father house is painted gray.

My answer is c because shouldn't it be both of their house right?

No.

http://grammar.ccc.commnet.edu/grammar/possessives.htm

OK so then A looks like a fit

Right. I had to look that one up to be sure. :-)

You are correct! The correctly punctuated sentence is C) My mother's and father's house is painted gray.

To determine the correct answer, we need to understand the rules for punctuating possessive forms of nouns:

When two or more people possess the same item, we need to use possessive forms for each individual before the noun. In this case, "mother" and "father" are each possessing the noun "house," so both need to be in possessive form.

To form the possessive of a singular noun, we add an apostrophe and an "s" ('s). For example, "mother's" and "father's".

So, option A) My mother and father's house is incorrect because it implies that the house belongs to both the mother and the father together, rather than individually.

Option B) My mother's and father house is also incorrect because it doesn't use possessive form for "father". It should be "father's."

Option D) My mother and father house is incorrect because it doesn't use possessive form for either "mother" or "father." It should be "mother's" and "father's."

Therefore, option C) My mother's and father's house is painted gray is the correct sentence since it correctly reflects that the house is owned by both the mother and the father individually.