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This could be flea bites, contact dermatitis, or another skin issue.
Since they all three have the bites, you know that the problem is not system and that it's a problem for all the dogs.
You should evaluate their bedding and wash or dispose of it.
You also need to see your vet for a prescription flea and tick preventative.
If this does not help, a vet visit will be needed to diagnose the cause.
Let me know if you still have questions.
Dogs can have allergies to grass, particularly when it goes to seed. I really doubt that all three dogs would be suffering from allergies, though, unless it's to fleas or products. It's not common for all three dogs to have the same symptoms if it's environmental allergens.
You can get frontline from your vet now without a prescription. You just walk in and can buy it over the counter.
The bumps sound more to me like a staff infection.
You need to make an apointment with the vet for one of the dogs and then you can probably get medication for the others based on what you tell the vet.