I couldn't understand the above sentence properly, especially the なんてないもの part.
I have looked for the meaning of 相手をする that can be translated as keep someone company or to take notice, and in my interpretation of the sentence would be "paying attention".
ないもの literally would be something that doesn't exist.
So, can I translate the sentence as follow:
"It would have been asking for the impossible for my brother to pay attention to me."
Thank you for the guidance.