Assalamolaykom... a) A son had graduated from the university. A family wanted to cook and send it to the mosque and ask the congregation to make a dua as to thank to Allah of their son's success. b) In stead of the first aoption, the family wanted to invite the family members and friends to their house, and read yassin, dzikr and dua in congrergation as to thank to Allah. c) A family just wanted to cook and give it as a sadaqah to the mosque with an intention to thank Allah but didn't want the congregation to make a dua or what so ever. Which of the above action is permissible in Islam. If none, what is the best the family should do to thank Allah of their son's success? Thank you

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.

Thanking Allaah for His bounties is something Islamically required; Allaah Says (what means): {Then eat of what Allaah has provided for you [which is] lawful and good. And be grateful for the favor of Allaah, if it is [indeed] Him that you worship.} [Quran 16:114]

Also, feeding people is a good deed as the Prophet   said: "O people! Spread salaam, feed the hungry, keep ties with your kinship, and pray while people are asleep (at night), you shall enter paradise peacefully." [Ahmad, At-Tirmithi and Ibn Maajah]

As regards the best option among the three options which you mentioned, then it appears that the first option and the last option are the best as they are free from any act that could be considered as an innovation like reciting the Quran in congregation and making congregational supplication.

Allaah Knows best.