AITA for not wanting to adopt my brothers child?

Mobile, sorry for formatting.

My husband and I are unable to have children. We have been together for 10 years and at this point we’re fairly content with our child free life. We have explored many options, such as fertility treatments which left us with a mountain of debt that we have just finished paying off. My entire family is aware of the issues we’ve had, since it’s been ongoing for years. They’re very supportive, but at times almost too supportive. My mother, to be exact, goes a little over the top sometimes when trying to figure out how we could possibly have a child. We have considered adoption, but the cost is outrageous. We are not open to fostering to adopt, although I know that would be a much more affordable option. On another note, my brother and his wife have two beautiful children that I love very much. My mother recently brought up in conversation that she would like to PAY my brother and his wife to have a baby and give it to me. To say that I was flabbergasted by this idea is an understatement. First off, why would they be willing to give up their own child? That seems like a crazy thing to even ask someone. Secondly we live half way across the country, so they would rarely ever see us, or their child, although I understand for all intents and purposes it wouldn’t be “their child”. But basically this kid would grow up with two siblings and would always believe that they were their cousins, and mom and dad are actually their aunt and uncle. That just seems like it would cause some long term emotional and psychological damage if they were to ever find out, which I honestly don’t think I could lie about that. Just the entire situation seems so uncomfortable and something I absolutely wouldn’t want to be a part of. I told my mother absolutely no way would I consider doing that. She in turn went behind my back and asked my brother and SIL anyways if it is something they’d consider. Luckily they both said no, they wouldn’t be up to doing that. Still my mother thinks I’m a huge asshole for not being willing to accept a baby no matter the circumstances. AITA here??