primary beneficiary vs secondary beneficiary

Hi, unfortuanately my dad died recently at the age of 84. He left me as his primary beneficiary in a small 403B IRA with USAA. He name my brother as the secondary. I called USAA and they are sending me the paperwork to fill out to transfer the IRA into my name so I can then removed the funds. HOwever, when my brother called ( secondary) they told him they would send him paperwork to fill out as well???? IF his name is on the 403B as secondary I know they have the right to discuss this account with him, but since I am primary then the funds come to me. So why are they sending him paperwork to fill out?

His wife, our stepmom couldn't get any information about it as she was not named at all , but CAN SHE dispute my being primary and ask that it be equally shared between me(primary) and my brother (secondary) if my dad wished it to be this way? Can anyone change it now that my dad is deceased? Just wondering why they would send my brother forms to fill out as well when he is the secondary only?

thanks