Or get (1) from a rich, old person with no heirs, do (2), and then once the involuntary parent dies (3) show up and use offspring from (2) to claim the inherita

Or get (1) from a rich, old person with no heirs, do (2), and then once the involuntary parent dies (3) show up and use offspring from (2) to claim the inheritance. At least here in Norway, children are guaranteed part of the inheritance regardless of the will.