will I receive discounted per line rate for Combining 2 separate multiple lines ATT UNLIMITED family plans into one

Yes. You can transfer the billing responsibility of 2-line plan to the owner of 4 line plan, which will create a 6-line plan. There are no additional discounts after 4 lines, but you'll get that rate on the 2 new lines, instead of the higher 2-line rate. Installment plans transfer with the number

You can definitely do a TOBR and move all lines to one account and you will definitely pay less per line for those 2 lines on their own account. I believe the per line rate for 6 lines is the same as for 4 lines. 

Thank you so much for your insights.

We'll be happy to provide additional context @AditiD.

As @sandblaster mentioned, you could do a transfer of billing responsibility (TOBR) to pay a lower rate on two of your lines. You can initiate the process via the TOBR portal. To move lines between accounts, scroll to and select Start a transfer. We’ll provide an overview and then ask you to sign in. After you sign in, select the account and lines you want to move. When we ask what you want to do with the lines, choose Move to a different account.

Please let us know if you have any additional questions or concerns; if so, we'll be happy to assist further. Thanks for reaching out to our AT&T Community.

Darais, AT&T Community Specialist