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Welcome to JustAnswer, my name is*****’m an immigration lawyer in the UK and I’m happy to help with your question today. First of all, I am sorry to hear that your brother is in this kind of situation, by law,
if circumstances change before the arrival, the Home Office has a right to decline his entry to the UK.
Although, unless the border officers also have this information, it is very unlikely to happen.
They will not "deport" him but will not allow him to enter the country and ask him to go back. Again, this is unlikely unless the sponsor specifically sends this information to the Home Office.
In this case, the Home Office may return him back at their expense but this is not good for a person's immigration history. It depends on an individual's case.
They also notice the Home Office, but because it has happened so shortly, border office may not have information yet.
I am afraid, I can not answer this question as I do not hold this information.
You are most welcome! I hope everything goes well with your brother's arrival.