Mistakenly receiving extra money into one's account

Q: I'm using a banking app, so I have transferred funds from 1 account to another but the transaction failed and the balance has been deducted from my account. After a few minutes, I received a refund but my 2nd account has also been credited with that amount... So I'm asking that should I return it to the merchant as I have been paid this extra amount mistakenly.

Second husband being a mahram for the wife's daughter

Q: I am getting married to a woman who already has a daughter, from a previous marriage. Would I be a Mahram for this girl, because Allah says:

وربائبكم اللاتي في حجوركم من نسائكم اللاتي دخلتم بهن فإن لم تكونوا دخلتم بهن فلا جناح عليكم

Would it be ok for me to travel with this girl?

Will Hazrat Isa (alaihis salaam) return to this world as a new Nabi?

Q: I have heard that when Hazrat Isa Alayhis Salaam comes to this world he will come as a Nabi. But I am confused because we know and it is mentioned in the Quran Sharif that Nabi Muhammad (Sallallahu Alaihi Wasallam) is the Seal of the Prophets and is the Final Prophet and Messenger, after him no new Nabi or Messenger will come to this World. Please clarify.