[Closed] Would you guarantee a mortgage for your brother-in-law?

I've been asked to guarantee a mortgage for my brother in law. He is living with his parents at the moment and can only afford a mortgage of X. To get the house he wants which costs more than they'll lend him he requires someone to act as guarantor.

His parents have given him some money for a deposit but have both given up work as they didn't like their jobs so cant't guarantee the mortgage for him. Apparently that means that it falls to me to act as guarantor.

My wife is also giving up her job in August to go and train to be a teacher so I will be the sole earner. I'm an architect for a small firm and job security is never great as we are constantly scraping around for new work.

I've no real reason to think that my brother in law will default on his payments but then if the bank doesn't think he can afford it there must be a reason.

Am I being overly cautious or even mean?

PS Sorry this has ended up in the wrong forum section!