Is it normal to let my sister do full body massage for me

To her, you are just another patient with as many people as she massages. With that said, I don't think it's the smartest thing as it could create some supressed sexual thoughts on either end and awkwardness between you two, but I guess it really just depends on the specific individuals as well as each of your looks and comfortability with each other.

To answer your question, you're not a freak or doing anything wrong, but I do think at least half of people would prefer someone else to massage them. But then again, I've shamefully always wanted a hot sister so it's honestly an attractive thought to me so take my advice for what it's worth.

Normal if she does no touch ur cock and massage your cock. Do you feel hard on when she touches you.? If not thn ok

It's only normal if the there's no inappropriate touching.