Apostrophe for Compound Nouns

There was a confusing question about “Apostrophe for Compound Nouns” on one of our competitive tests; I would like to know the correct answer. The question was:

Which one of following sentences is the correct one?

1. Mother’s and Father’s new cars are identical

2. Mother and Father’s new cars are identical.

I searched the internet. Both answers can be correct based on (separate or shared) ownership. I have copied internet references below. I think if Mother and Father share the ownership of new cars together, the answer #2 is correct. If Mother and Father are legally separated and have separate ownerships of cars, then answer#1 is correct. I think that both answers should get marks. Teacher should give marks to both answers because enough information is not given to choose appropriate apostrophe.

References:

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

When you are showing possession with compounded nouns, the apostrophe's placement depends on whether the nouns are acting separately or together.

a. Miguel's and Cecilia's new cars are in the parking lot.
This means that each of them has at least one new car and that their ownership is a separate matter.

b. Miguel and Cecilia's new cars are in the parking lot.
This construction tells us that Miguel and Cecilia share ownership of these cars. The possessive (indicated by 's) belongs to the entire phrase, not just to Cecilia.

2. http://www.grammarbook.com/punctuation/apostro.asp

Use the apostrophe and s after the second name only if two people possess the same item.

Examples:

Cesar's and Maribel's job contracts will be renewed
next year.
Indicates separate ownership.



Cesar and Maribel's job contracts will be renewed next year.
Indicates joint ownership of more than one contract