Is it permissible to give the alms I have designated weekly to my family instead of the poor?

Voluntary acts of worship do not become obligatory merely by pledging them, unless the pledge is a commitment or a covenant with Allah. It is best for voluntary charity to be given to family and close relatives if they are in need, as the Prophet (peace and blessings be upon him) said: "The greatest in reward is that which you spend on your family." And charity to relatives is both charity and maintaining kinship ties. However, if the pledge was made to Allah Almighty and you uttered it, it is an oath and a vow that must be fulfilled, and the portion designated for charity must be given to whomever you specified. If you did not specify anyone and it was not a vow of requital, it is permissible according to some scholars for you to include your family and benefit from it yourself, although it is better to avoid that.