Possessive 's
The cat of the kid.
The kid´s cat
The computer's teacher is there.
Incorrect.
The teacher's computer is there.
Jack and Rosie's baby is 1 year old.
The baby is of both Jack and Rosie.
The computer of the teacher.
The teacher's computer.
Susan's cat is up there!
Correct
Mark and Tanya's cats died last year.
The cats belonged to BOTH Mark and Tanya.
The kids of Marco.
Marco's kids.
Samuels restaurant is awezome.
Incorrect.
Samuel's restaurant is awezome.
Mary's and Paul's apartments are old.
1 apartment for Mary and 1 apartment for Paul.
The toy of the dogs.
The dogs' toy.
The kids's toys are here.
Incorrect.
The kids' toys are here.
Jen's and Laurie's kids are friends.
The kids of Jen (kids A) and the kids of Laurie (kids B) are friends.
The cat of Marco.
Marcos's cat.
Correct
Peter and Karl's theory was crazy.