Sorry to burst your bubble but using your neighbors wireless internet without their knowledge or permission IS stealing however you try to spin it. The lemon tree analogy isn’t quite accurate but nice try.
If you truly feel that you are in the right, knock on their door and tell them what you are doing. If they have no problem with it, cool. If they do, it just proves my point.
I had an unencrypted wifi access point up for awhile and found several of my neighbors connecting. It pissed me off so I kicked them off and locked it down.
On another note, Slingbox would probably take exception to you using your family members service, regardless of whether you have your family members consent or not. It’s slingbox that has the arrangement with your family member. It would be no different than a family member living next door letting you tap into their cable tv. I’m pretty sure the cable company would frown upon that.
I find it interesting that someone who is supposedly religious is defending a couple of obvious examples of theft. I guess that the moral bar is set pretty low these days.