A: Mom and her sisters have decided to go on a trip together
for B it should be: His uncles and my brother were going on a camping trip
for C: the wording is just funky.
for D it should be: Both Natalia and Mike have invited us over
Hopefully this helps and good luck.
The answer to the first is B. Appositive position, because it is separated with commas. The answer to the second is C. predicate position, because Frustrating is a participle that combines with is to create a predicate.
The correct verb usage is My mom recommends that he get a cart before going in.