For the most part, I really see no harm in it. If they are tiny pieces, they're not likely to choke. If you are already putting cereal in their bottles (like you said in your bio) they are actually more likely to choke on that honestly b/c bottles are not meant to have "chunks" in them. Since you are putting cereal in their bottles, perhaps they becoming ready to eat.
If your dh wants to feed them, then buy some baby food. There is a general rule of them as to when it's "acceptable" to start baby food - BUT every baby is different and has different nutritional needs. Ideally you should start w/ cereal (about the thickness of instant mashed potatoes/baby food).
Mostly, I want to say, you've mentioned your husband works a lot. I understand that what you are seeing is him "defying your rules" by feeding the twins, but I also see that perhaps thats one of the ways he is trying to be involved and bond with his children. Perhaps it's not the "best" thing for him to do, but at least he's doing something. It sounds like he does not have as much time with the kids as you, so of course he may not know them as well, but it's important that he be allowed to make decisions concerning the twins as well. Afterall, they are his kids too. If he wants to feed them tiny pieces of food on occasion, they'll live. If you are concerned about food allergies (is there a history in your family?) - then let him know that he should not feed them egg, seafood, or peanut products (like peanut butter).
If it really concerns you that much, then the two of you should sit down and talk about what is and isn't acceptable for the twins. It shoudl be a conversation w/ mutual input, he should be allowed to make decisions concerning the kids also.
I'm certainly no expert, but I am a mom of 4 - whose kids all lived despite daddy AND I making a ton of mistakes :)
Good luck to you all :)