My understanding is that there is a limit to how much you can safely chop off each year without damaging the tree. If they've gone 10 years without pruning you may have to spend the next couple of years getting them into shape.

I prune my apples and pears now, while they are dormant. Once they reach full size (as big as I want them to be) I will also prune in the summer or twice each year.

I would take out any obviously dead or damaged branches and then prune everything back to last years growth. You should be able to look at each branch and see the smoother - less corky bark. On my trees they can send out 3 to 4 feet of growth each year. Your goal is to get the trees to make fruiting spurs (short stubby branches where the blooms and fruit will be). They don't tend to make spurs on thick branches or on new branches - more like 2 year old branches. If you want your trees smaller you may have to prune hard and wait a few years before you get spurs on the newer growth.