I pray to Allah to forgive your mom and admit her into His mercy and paradise.

If you are asking whether you can take out the Fidyah from her estate you may do so without his permission. If you are asking whether you can take his money, you are not allowed to touch it without his permission.

So, I would advise you to approach him gently; if he still does not agree to give, then you should give whatever you can afford to and leave the rest to the mercy of Allah. Allah does not burden anyone beyond the limits of his or her ability or means.