When I lived overseas, I used a VPN client that gave me a US IP address. I used Hotspot Shield, but for a whole list of them, see
here. Many of these are free because they are ad driven, but Firefox with AdBlock plus filtered out the ads for me. It's generally best to launch your VPN before you start browsing for a book; some websites, like B&N, look at where you're from when you arrive.
For free books, see
Inkmesh for promotional ebooks. If you still have a card and your library offers ebooks, that's a viable source. Some libraries, like Philadelphia's, will sell you a library card for a nominal fee.
The ability of family members to purchase on your behalf depends on the format. ADE books have encryption applied at download. If your family has a different ADE account, their books won't work on your device. I believe that's the same with Kindle; if you're all registered to the same account then you can access them. If you have a US credit card and run a VPN, you should be able to purchase at most sites.
A visit to the Apprentice Alf blog will give you the tools that you need to remove the encryption. With the encryption gone, you can easily convert the book to the format that will work on your reader.
If you haven't picked a reader yet, a visit to the
matrix might help. I'd stay far away from the Nooks, as B&N is very stringent about not supporting them overseas, even to the point of not permitting updates.