Answers:
yes you can go and get within trouble doing this, i would stop doing this or ask them and see if it is ok.
if you borrow it beside personality yes its ok, if character doesn't suspect, later its unofficial to any extend. but again if you see any sympathetic wireless net, it shows i.e. not your guiltiness, its other party ignorance.
Technically Yes, it's stealing. You can be traced by IP address, the one-off address every computer transmits. Thats why you should never articulate anything on a message board that you wouldn't utter within public because it's adjectives traceable.
Without their assent, it is unofficial. It would be similar to sneaking over to your neighbors house and patching in to their cable so you can monitor TV short paying. If your neighbor will tolerate you, perchance share the cost of his wi-fi, consequently it is OK.