So if one man sired two separate children, to twin sisters, would the children be more like siblings genetically?

If the sisters are identical twins then the children are genetically full siblings.

If twin men and twin women have children together as separate couples, the children are full siblings genetically.

This would make a good mind puzzle. How can I be someones cousin be full siblings when we are born from different fathers and mothers.

This kind of is a weird way to come at this question… the children could never “technically be siblings” because their mothers are not the same person. We don’t define words like son, daughter, mother, parent, sibling in genetic terms.

Genetically, children of two twins by the same father have access to very, very, very similar combinations of genetic material. But not quite exactly the same. What your question boils down to is, “Are identical twins genetically identical?” And, it turns out, they’re not exactly identical.

So, they wouldn’t “technically be siblings” in a genetic sense, either.

The answer is yes. I’d be willing to test this experimentally if you guys know of any hot twins that are interested.

@dappled_leaves Genetic testing would not be able to decipher who was the mother. Both children would get results of being a likely child of each women. The siblings also would share so much DNA they would be considered probable full sisters. The testing using statistics of a certain percentage of match from what I understand. My sister and I share very close to 50% of DNA. We share the same with each of our parents. If my mom had a twin I would share the same with my aunt, while usually I would share less with my aunt. A DNA test could not tell which was my mother in that case. It can be broken down even more than that, but I’m not very familiar with it.

@JLeslie You’re right, a DNA test would not be able to tell the difference. That does not mean that there is no difference. On the sliding scale of “could this person pass for a sibling?”, this case is on one extreme end. But the child would never literally be a sibling.

This is one reason that I said this is a weird question. I don’t know if the OP is asking whether a DNA test would show that one was the mother and the other not. I don’t know what “technically be siblings” means to the OP.

Yes, they are literally genetic siblings. I don’t see why you are saying they aren’t? The OP stated she realizes legally they are half siblings. We wouldn’t call them full sisters either to define their relationship, but genetically they are the same as full siblings.

@JLeslie I’ve already answered your question. Identical twins are not genetically identical as adults. They are very close – closer than any two people can be. But not identical.