i need help

to cut the story short my parents mortgaged our house and lot to a private individual without any papers signed, as in mere plain and verbal loan agreement only wherein my parents borrowed P400,000.00 with the original tax dec. as security..3 yrs after, my brother's parents-in-law volunteered to pay the amount of P700,000.00 as full payment of my parent's indebtedness (the P400,000.00 plus the agreed interest therein for 3 yrs) with the verbal understanding that the house should not be sold to other people..and that said property would be used by us their children...we as heirs protested when they did not allow us to consider their generosity as conditional mortgage.. instead they executed an absolute deed of sale which my parents signed and we allegedly were defrauded to sign because then, they let us sign a blank paper except for our parents who signed the real document it was against our will but our parents will were to be followed..they were able to transfer the title in their name..and were successful from ejecting us all from possession...after 10 years do we still have the right to recover the property? because in reality they only got the property for P700,000.00 considering the actual market value of P3million 10 yrs before. or at least to ask for additional amount..