If a Musi already paid Hissa Jaidad on their house during their lifetime, are heirs required to pay again after demise?

No. If a Musi paid Hissa Jaidad during their lifetime, the heirs are not required to pay again on behalf of the deceased.

However, once the property is inherited, it becomes the property of the respective heirs. If an heir is a Musi, they are required to pay Hissa Jaidad on their inherited share at their own Wasiyyat rate.