I only download songs when an older sibling buys it for me, but their itunes account stinks and the song(s) wont work on the computer (*cough* samwise *cough*)
But, then it's technically not illegal because i already own the song.

Most definitely not illegal. it's not really the downloading that's illegal anyway. It's only whether you have a legal (or maybe moral but right now we're dealing with legal) right to what you have acquired. In this case you would be beyond reproach!