Hi
If contents of the document i.e., MODT submitted by them with forged signatures of your father are not changed, then you have two options:
1) Instead of raking up an issue check the entire documents and ask your father to affix his signature after cancelling the forged signature and proceed by putting an end to probable litigation and/ or repercussions thereof.
2) You stop at this juncture, issue notice to them for forging the signature of your father's signatures and the same leads to unpleasant situation and leads to civil and criminal disputes which will not only coast you substantial time, and expenditure (if the contents of MODT are in any way changed).
Now it is your discretion to choose between option (1) or (2).
Good Luck