I would describe both of your kittens as brown mackerel tabby domestic shorthairs. Mackerel tabbies have relatively narrow vertical stripes, typically with some of the stripes broken up into spots. Mackerel tabby / broken mackerel tabby is the "wild type" which means it is believed to be the original color and pattern for the domestic cat. You can imagine your cats stalking mice and rats around the ancient granaries, 8,000 - 10,000 years ago when cats first domesticated themselves
I notice that you included several pictures of your cats' spotted bellies. Many times people see these spots on the belly and wonder if their cats are related to the Bengal breed. Spots on the belly are a normal part of the mackerel and classic tabby patterns. These spots don't indicate that the cat is a spotted tabby, or that it is related to one of the spotted breeds.
Most cats are not any particular breed, and are not "mixes" of breeds, unlike dogs. But that doesn't make your kittens any less gorgeous or special -- they are beautiful kittens and I'm sure they will grow up into beautiful adult cats!