Every new account set up on Ancestry.com requires it's own email address. So no, the invites aren't sent to my email address, they're sent to new email accounts I've set up.
1- You set up a gmail, yahoo, whatever is your pleasure free email account.
2- I find it easier and it works more often to invite by user name.
3- I log off MY ancestry.com account, and then sign up for a new (free) ancestry.com account, using the new email address. I pick out nice name and easy to use password, tailor it to the person you intend it for.
4- I sign off the new account when I'm finished, then sign into mine, and extend the invite to the new account using the new user name.
5- I sign off my account and sign into the new account, and check to see if my tree is in the new account's Family Tree pull down menu.
At this time I also customize the new account's home page, adjust preferences, alerts, etc. I make it look as easy and clean as possible.
6- If it is all's good, I send my grammy or other tech challenged relative a regular email with the hyperlink to ancestry.com, and instruct them where to enter the username and password (also in the email) and to hit "sign on" after they enter those two things.
It's work for you, but I can guarantee less time than trying to walk someone through the process. It's also great to be able to set up their home page so they can see your tree front and center after they sign on.