As long as you have an insurable interest in another person, you can buy a life insurance naming that person as the insured under the policy.
And, as long as you answer the questions truthfully on the application for life insurance, and let the insurance company know how much life insurance the person is insured for total among all policies on the person, so the insurance company can understand if the person is over-insured, then there is no problem with having more than one life insurance policy on a person.
If the person is over-insured, the insurance company will let you know when applying for the life insurance and answering the question about total life insurance coverage the person ahas already.
Here's an article that explains how many life insurance policies can you have.