Wa `alaykum as-salamu wa rahmatullahi wa barakatuh

 

Your brother who is a Muslim can definitely act as your wali. The person who told you otherwise is wrong. He is also wrong in saying that your father’s marriage with your Christian mother is not deemed as valid. The marriage is perfectly valid as stated in the Qur’an: See for instance:

 

 “Today, all the good things of life have been made lawful to you. And the food of those who have been vouchsafed revelation aforetime is lawful to you,  and your food is lawful to them. And [lawful to you are], in wedlock, women from among those who believe [in this divine writ], and, in wedlock, women from among those who have been vouchsafed revelation before your time -provided that you give them their dowers, taking them in honest wedlock, not in fornication, nor as secret love-companions.  But as for him who rejects belief [in God] – in vain will be all his works: for in the life to come he shall be among the lost.” (Al-Ma’idah : 5: 5).

 

So, you need not feel any inhibition in asking your brother to act as your wali.

 

Before concluding, it is important for us to know that we are not allowed to speak on matters of religion without proper knowledge. By doing so, we may incur a great sin akin to associating partners with it – as Imam Ibn al-Qayyim has rightly said.

 

Allah Almighty knows best.