Awaiting expert input, but couldn't resist an attempt at using my school Latin rusty after '40 + years and more', to get the ball rolling... Beginner's humble effort...
One thing I think for sure is that the length of time is '4 X 20' years and ultra = beyond..so eighty years plus..a life time and more, by implication.
It seems to be a joint 'willing' (dicunt plural : they both state) or 'granting' that after death of the afforesaid (insuper) Rico Ratcliffe, ,son and father , also named Rico the rights should pass through legitimate male heirs (of the body (corpora) of the Miles (Soldier, Knight) for the time stated.
A little confused by Mandia with capital M , but am guessing this might mean by order or mandate , rather than name of a third party???
As I say I await to be corrected here,
Chris