You proposed it.

Wow, they could accidentally cheat on each other and not even know it.

Depends on how "identical" they really are.

Identical is absolute, unless you�re talking about some add-ons.

If both sets of twins are identical, and they each have children, are the children not essentially siblings biologically? It�s been about 20 years since I took high school biology.

Wrong.

This reminds me of a day in my family law class, where Judge Spurlock was talking about the one situation where it was impossible for the mother to prove paternity through a DNA test.

Identical twin brothers.

I'll let y'all think about the implications of that for a bit.

I'm sure they're already on it.

Then the wrong word is being used. Identical is an absolute. Have scientists decided that identical twins do not have identical DNA? It was thought they were 100% identical, but studies were done showing that might not be the case. I don�t see a consensus on it.

Edit: See link below. Seems weird to me that they can�t compare DNA between identical twins and either get a 100% match or not.

https://www.scientificamerican.com/article/identical-twins-genes-are-not-identical/

I played football with two identical twins. I assure you, the were not identical in the showers. Also know a guy who 'dated' identical twin sisters without their knowledge. They were not identical, either.

Yes, you get an A+

Like one of them told funnier jokes?

Yes, the answer is very complex and not completely understood.

Genes are turned on and other genes are turned off as an embryo develops.
With "identical" twins, the embryo divides in two at an early cellular development stage.
The maternal uterine environment then plays a significant roll in which genes are turned on and which are turned off. One of the divided embryos may have more fortune than the other and grow healthily. The other may not make it to fetal stage at all. If they both survive, differences in that environment may have turned some genes on and some off in the now two separate developing embryos. There's multiple other factors such as variances in the maternal messenger RNA in the now separate developing embryos. Messenger RNA takes the information from the nuclear DNA and transports it to the the cellular cytoplasm for protein synthesis. If the maternal messenger RNA is different in the two growing embryos, different proteins will be made from the same DNA--thus early phenotypical differences between the two "identical" twins--see Fouzman's examples.

Weird