What if you find out your dad's account has only 1 BTC if you are going to give anyone 5-6 BTC?
If you do have some time on clicking out that image link on OP, then you wont really be saying up such thing.
Checking it out which the wallet that does 26 BTC and giving out 6 BTC as a reward on cracking up the password then it is really that a generous reward i should say.
@OP, just like the rest been saying on trying out those wallet recovery service out there but of course stick into those known ones.
Just like been mentioned too that you should have at least having some small detail or information about the password
because if we are talking completely having zero information then consider these coins to be lost already. There's no way on cracking on this one i should say.