I have 2 separate faucets in the kitchen, bathtub and bathroom sink for hot and cold water. The cold water runs fine but there is only a trickle out of the hot water faucet. This occurs on all three sets of faucets. What can be wrong?

I'll bet you don't run maintenance on your water heater and now you're paying the price. Minerals built up in your water heater has built up to the point that it got sucked into the faucet hot water seats where they're blocking them. The solution would be to shut the water off to the faucets in question. Open up the hot water side and clean the seat. Clean out any trash you find in there. Before you button up place a wash rag over the open faucet and turn the water back on to flush out the valve body and the supply. You should have a full stream of hot water. If not click on back. Do this on each faucet.
Now let's see about getting the minerals out of your heater.
For long life and fewer troubles you should keep your heater clear of mineral build-up by flushing on a regular schedule. Attach a hose to the boiler drain at the bottom of the tank. With the pressure on, open the boiler drain and let it run until the water runs clear. You will see a spurt of red,(rust) followed by white or yellow grains,(lime or calcium carbonate). This shouldn't take more then a few minutes. Don't forget to flush it out every month. Your heater will thank you for it. Hope this helps, Tom