When the front tires on one of our cars wear on the inside, is it a sign that the toe-in, caster or camber is out of spec.?

First off caster does not cause wear. Negative camber wiil wear the inside if excessive. Not enough toe in or a toe out condition will greatly accelerate wear with negative camber. .10-.20 total toe in with -.75 to 0 will seldom wear excessivly on the inside. This assumes all components are in top shape. As the car goes down the road it is trying to push the tires outward at the front. If your static specs are correct and you have worn components it will toe out untill the slop is taken up. What started as .10 toe in could now be .50 toe out. Then you have wear and the first thought is to blame negative camber. All this being said I try to shoot for -1/4 to +1/4 camber, as much positive caster as I can get,.10 to .20 total toe in.
Doug