When selling on a land contract can you put in the land contract that the buyers can not sell on a land contract until there land contract is paid off ?

Yes, you can require in the contract that they be the person living there, that they can't lease or rent or sell.

The big issue is that they really can't sell it on a contract if they are in a contract. Since they don't own it, the first seller owns it till the first buyer pays off the contract. So the first buyer can't really sell it, if he does not own it.

You could allow him to have someone else take over the contract if you want

They cannot sell the property whether you put it in the contract or not. A land sales contract occurs when the seller retains ownership until the terms of the contract are fulfilled. Otherwise it's a mortgage not a sales contract.

You can put in the contract that they cannot sell or transfer the contract without your approval.