I had that Powertec gym that you have decided to purchase. I would say in general it is much more solidd than I would have expected, with one exception. The plate that you stand on to squat is thin, and would bend alarmingly when I got on it -- I was 210-220 at the time and never squatted on it with mroe than 150 lbs. max.
Also, I developed a shoulder injury, I think it might have been from benching heavy on the machine, but I don't really have any idea.
One thing I appreciated about it was that the motions -- especially on the lat pulldown and the military press -- were different than I was used to but seemed more effective and more natural (i.e. the lat pulldown seemed to hit my last more, and the military press forces you to push more or less directly over your head).
But my concerns are fairly minor, especially since you can do your heavy squatting and benching elsewhere, and having this option might encourage your family to do those exercises.
If you're concerned about durability, I think this is the ideal machine to purchase. It's very well built and quite strong -- I'm sure you've seen the specifications.
If you have any specific questions about it, feel free to pm me if you'd like.