forget the whole idea. get some cash off grandpa when you see him. if you have to cover some short term expense then so be it. anything else will be a disaster.
i know loads of people like this. they can't be trusted to buy a plastic bag off amazon without ordering a 50ft fibreglass elephant. someone like that could not obtain and send bitcoin successfully if your life depended on it.
First of all it was a giraffe you dang whippersnapper. Secondly when I was in the army my platoon was marching... Zzzzz
I do believe if you email grandpa a link to download any software where you can control his screen you'll be set. Just don't let him do anything then you don't have to trust him! After you send yourself the $1000 (or whatever) transaction he can play around if he wants to with tiny amounts and lose it all somehow haha.
