@oristarA,
Quote:So "any property that is considered by law or custom as inseparable from an inheritance is inherited with that inheritance" mean "any property that that is considered by law or custom as inseparable from an inheritance is inherited with that inheritance"?
No. I don't know why you want to insert the extra "that". The sentence works perfectly well without it, and it's inclusion is wrong.
You could write it differently, if that would help:
Any property which is considered by law to be inseparable......etc.