Is it permissible for a Muslim to dispose of his wealth before his death (such as gifting it to his wife) while there are legal heirs, and what is the legitimate proportion for that, and is the limitation to one-third restricted to the will?

A man is not permitted to make a bequest to his wife, due to the Prophet’s (peace be upon him) saying: "There is no bequest for an heir." If he does make a bequest to her, the matter is left to the discretion of the remaining heirs. If they approve, then it is permissible; if they do not approve, then it is not.