first thing you have co-branded and you apply add-on for your brother that i didn't knew you could apply add-on for co-branded cause it a ok card i hope it infinity variant and your brother will get pre-approved offer on this saving a/c but might face issue on approval cause as you might know taking co-branded cc from hdfc as your first cc from hdfc is a no-no, you're giving him co-branded add-on in this case so yeah good chance he might not get a core hdfc cc on his own now. don't worry thing happen take the add-on use it, worry about this later. this is my pure knowledge guess. i could be complete wrong too. cause i haven't heard of such case before.