Why is my agent telling me that I need to also take out a separate insurance policy on the house in addition to the one that is already included in my rent.
is this legal?
More information is needed before being able to answer your questions. It is possible that the money you are paying, which is supposed to cover insurance and taxes, is being pocketed by the seller. You should get some kind of receipt for payment of both items, to make sure that you are not in arrears. There are all kinds of scams involving land contracts and by the time the buyers find out what is going on, it can be too late.
If your agent is insistent on you getting additional coverage, he should be able to explain to you why this is necessary. Whether or not it is "required" would depend on the facts of the situation.