You can activate up to 10 lines under the same account details. Simply login at https://www.unrealmobile.com/login and then head over to https://www.unrealmobile.com/plans & select PLANS at the very top to buy a plan with an eSIM.
To buy a new phone head over to https://www.unrealmobile.com/shop/iphone
Make sure to login to the same account during the activation process to attach those products to your account.
Whenever you log in at https://www.unrealmobile.com/login, you will have the option to switch between each line under your Account Dashboard.