Which verb completes the sentence?

Because Grand Mother and Grand Father, when taken as one unit i.e. Family, it should take verb ---Does.

Do

In a question, the subject comes after the verb: grandmother and grandfather (2 subjects joined by and). To review, see Troublespot 2.The subject comes after the verb. (Remember, to see if subjects and verbs agree, find the verb first and then ask who or what does it? to find the subject.) See also Trouble Spot 4.The sentence has more than one subject.