Can't register sims 3 game bought on origin?

I bought The Sims 3 Island Paradise Limited Edition, and after a lot of struggle, I've managed to install the free stuff pack and carnival costumes pack , but I can't seem to manage to install the Island Survival Pack. Unfortunately, the game was ordered on my dads account, so the stuff pack and expansion pack are both registered as his games,- apparently if your origin and sims 3 account emails are linked, if it's installed on origin it'll automatically register on the sims 3 website?- so I can't use that. Whenever I try to register either the expansion or the stuff pack, it comes up with invalid code because it's already been used on origin? What's the point in having a code to register when you can't use it... Also, pack to the survival pack, you can't install that without the island paradise expansion pack registered on the sims 3 website, but I can't do that with it telling me the code is invalid. How can I get around this? (NEVER ordering an origin download, or origin at all, if this isn't sorted out)