I'd say it was eminently legal to install a game on as many machines as you own. If it's just you and yours playing, that's entirely fair use -- not that reasonable or fair have ever stopped some idiot copyright lawyer from filing suit. But at least you'll have a situation that will embarrass the hell out of them should it get before a judge.
They'll probably never know and they've sure got better things to do with their time and money. But like I said, reasonable or fair doesn't enter into it.