Well first of all, baby Henry/Philip/John (not sure of the name) would have a pretty fantastic inheritance, as the marriage contract between Mary I and Felipe II stated that their son was to inherit not only England and Ireland, but also the Spanish Netherlands. Considering that the Spanish tried to detach the Netherlands several times, that should work well. Now, second, everything will depend on dates. You have the Prince of Wales born in April /May 1555 (the estimated date for Mary to give birth according to her doctors), a year or so before his grandfather abdicated and divided his lands between his son and brother. Now the marriage contract made Mary's son heir of England and the Netherlands, so I'm not sure if the Netherlands passes to Felipe or directly to his son (depends on what Charles wants to do). What happens to the Netherlands is a big deal, but I'll come back to that later. Right now we're focusing on England. This brings us to Lady Elizabeth.