Sister cats - one pregnant

I have a friend who has two cats which are sisters. One has become pregnant. When she has the kittens, will there be any behaviour problems to look out for from the other sister that he should be concerned with?

You should get the one cat that is not pregnant spayed ASAP! Once the kittens arrive and a little before, separate the two cats because most momcats become quite possessive over their new family. Once the kittens are old enough to roam around there should be no problem in putting all the cats together. Please keep the pregnant cat and her sister indoors as well from here on in. It is so much safer for them to live inside, and once the kittens are born, the momcat will go into heat and could become pregnant again-