Yes, you may purchase impression kits and aligners for more than one individual. The best way to do so is to make sure each individual's account is tied to a unique email address, regardless of who made the purchase.
While They are actively working to allow a single user account to manage multiple individuals, for now, you'll need to purchase each kit under a different email address to ensure proper prescription and monitoring of each treatment. If you only have one email address, there are many free email services available that you can use.