Is donating a fifth of one's salary, based on the verse "And to Allah belongs the fifth of what you acquire as spoils," considered a Bid‘ah (innovation)? Is it permissible to give this money to younger siblings to help the father with tuition fees? What are the proper channels for charitable giving?

The intention to donate one-fifth of one's salary is legislated in the sense that it is a charity and not an innovation. However, using the verse (And know that whatever of war-booty you may gain, verily, one-fifth of it is for Allah) [Al-Anfal:41] as evidence is incorrect. It is permissible to donate any amount of money to help a needy parent, and this may even be obligatory. The recipients of obligatory Zakat and charity are specified in the verse (Indeed, [prescribed] charitable donations are only for the poor, the needy...) [At-Tawbah:60]. As for voluntary charity, it is preferable to give it to needy relatives, as the Prophet (peace be upon him) said: "Your charity to a relative is both charity and strengthening of ties."