He is not permitted to do so, and she is not permitted to allow him to have intercourse with her.
Your previous Taqleed is valid and you can continue to follow his Eminence.
The dua (supplication) is asking Almighty Allah. The imams of the Ahlulbait are intercessors to Almighty Allah and Almighty Allah does not reject their intercession. Nothing is wrong in seeking intercession from the Prophet and his household (peace be upon them). It is mentioned in the Holy Quran that Almighty Allah had said: â€œAnd if, when they had wronged themselves, they had but come unto thee and asked forgiveness of Allah, and asked forgiveness of the Messenger, they would have found Allah Forgiving, Merciful.â€ (4:64)
If the fish that is used in the making of such products is halal, it is permissible to consume such a product. If it is not then it is not permissible to consume it.
If the other person at the restaurant was considered to be the buyer and customer, one is allowed to pay on his behalf. However, if he is paying for the other person, while considering himself to be party to the purchase, i.e. the actual buyer and customer, then he is not allowed to do so.