How to stop 3-week-old puppies from sucking each other's genitals?

You will need to separate Misty from the others or there could be serious damage to the other puppies' genitalia. This is probably from being separated from mom at a young age. You could try giving Misty a stuffed animal or a blanket to redirect her - she may suckle on these things instead.

This is usually not a hunger-driven activity in a 10 week old kitten. It can indicate that the kitten was weaned or taken away from its mother too early. I would definitely continue to prevent this behavior, as it can continue into adulthood and could cause problems like an infection in the mammary gland of your dog. You may have your dog wear a shirt to cover the nipples, or keep them separated unless you can monitor them. Since it can be brought on by stress, you can try supplements for stress such as Zylkene or Feliway/Comfort Zone Feline Pheromones. Here is some more information: https://www.petplace.com/article/cats/pet-behavior-training/wool-sucking/

This sounds somewhat unusual. If the skin is raw where the mother has been licking, then the pups may need to be separated from her until it has a chance to heal. You can still allow them to nurse under supervision several times a day, or you may need to bottle feed them if she won't leave them alone while they nurse. I would recommend having a vet take a look at the puppies to make sure that taking them away from mom is necessary, and they may also need antibiotics depending on how raw the skin is.

It may be that your dog is just fascinated with the nipples hanging down, or some dogs especially ones that were weaned young may still have that nursing instinct. Unfortunately you don't want them to nurse on her because it could cause trauma/infection. I would consider getting a dog shirt for her to try to help cover up the nipples and discourage your staffy from this behavior.

Do not allow the puppies to suckle on the dog that is not their mother. She is getting mastitis (infection in the mammary glands). You need to keep them separated. You can try home treatment for the mastitis with cabbage leaves (see link below) but she may need to see a vet for systemic antibiotics. ( https://vcahospitals.com/know-your-pet/mastitis-in-dogs )

If she stopped feeding them suddenly then mastitis would be a risk (she may refuse them because it is painful or the excess milk after she stopped could cause the problem after). If she is off form, has any fever or her milk glands are red, hot or painful to firm touch then she will need prescription treatment from a vet. If everything is otherwise good, just monitor for any changes. 48 hours of very light food if she is healthy and not underweight can discourage active milk production but do not starve her

This is normal behavior for kittens and they typically outgrow this. There is not much you can do in the way of training other than separating them. If you can find kitten clothes small enough to fit him, this could help too. Make sure to exercise them well. I hope this helps.