How do I keep kitchen cabinet AND closet doors from swinging closed

Boy, most people have the opposite problem. People leaving cabinet doors open then someone banging their head on it. I would believe your cabinets and doors are balanced to close. You would have to take them off and reset the hinges.

You probably can't. Though not visible to the eye sounds as if they aren't level front to back. Use a small level to find out. No level? Try a glass of water.

The two previous answers are good but here is something else that might help. For the kitchen cabinets you purchase stay open hinges that are very easy to install. of course it also depends on the type of hinges you currently have installed. if you have the European style you can actually adjust them.

For the closet doors, if you are able to balance them, you can install small wool slider type buttons that will soften the closing if it is closing hard. If you noticed that the door is actually out of balance, you could drill a small hole in the top or bottom and insert small weight of some sort to adjust the weight. For the weight you could use fishing weights or anything you can find that has some weight to it in a small space so you do not have to make a big hole. Seal the hole with a bit of two part epoxy.

soft closing add-ons are great for the doors. They are easy to install and available at most hardware stores and online.