's for two guys

[atabitaraf]

1. Jack, John and their brother's properties were held...
2. Jack's, John's and their brother's properties were held...
3. Jack and Jill's (store)
4. Jack's and Jill's (store)
I think all of them are gramatically correct but the odd styles (1 and 3) seems more natural to me, do I feel right?
(Please mention both in speaking and writing)

[philo2009]

Normal practice regarding compound possessives is to attach the apostrophe only to the last item in the phrase, leaving the others uninflected. There are, however, cases where this can result in ambiguity. E.g. in

I met Peter and Jack's father the other day.

it is unclear whether I met two people (1: Peter, 2: Jack's father) or simply one person who was the father of both Peter and Jack.

If the intended meaning in fact were 2, then, as infelicitous as it may sound, only

I met Peter's and Jack's father the other day.

would be clear.