is it normal to want to watch my husband have sex with my mom

Most of the time it isn't normal for a girl to want to see her mom get fucked by her husband. But their are some chicks that do like it. Just like their are mothers and daughters that fuck guys together and stuff. Depends on how your raised or if you watch them kinds of porn, etc and then start to like the idea. Asking her could either be fine or really bad. I'd def consider how she would respond to such a thing before even asking her, also consider how good of a relationship you two have. Their are people that hide their thoughts really well tho too. She could either get grossed out about it or be perfectly fine with the idea.

It's the most normal thing I've ever heard of.

yes it is very normal. Everyone wants to see their parents have sex... (rolls eyes)

Of course it's not normal. Good luck with that though.