Active Directory FSMO Role Transfer during Child Domain Migration

We have Active Directory Domain Structure as below.

- Domain Controller

PDC : XYZ.COM

BDC : XYZ.COM

- Child Domain Controller

PDC : A.XYZ.COM

- Child Domain Com

PDC : B.A.XYZ.COM

BDC : B.A.XYZ.COM

We are Planing for Migration little confusion in transferring FSMO Role.

First we will migrate XYZ.COM and it will holds all 5 FSMO Roles than we will migrate B.A.XYZ.COM for that which role should be transfer during migration?

Right now B.A.XYZ.COM holds PDC, RID, and Infrastructure Master roles.

Thanks,

Rigel Networks