2)There is no inheritor of the original ger.
That is your assumption, not Tosafos. Nevertheless, I am saying that you put everything into one person and there’s no reason to think Tosafos did the same. We don’t want you to treat this particular fellow like a full fledged ????? ?????? because of what will happen to the other ????? ?????? who might do Yibum when they shouldn’t while those who should won’t.
Or, if he said that this son should Yarshen the loan then the two are not mutually exclusive.