for all you doctors and heredity experts: can cousins be closer to siblings under the right circummstances?

Question

Say you have 2 sets of siblings: 1 brothre and one sister each. In the first set the brother's name Max and the sister's name is Sue, in the second set the brother's name is Kent and the sister's name is Maggie. Each set are full brother and sister and have the same bloodlines for each family.
Max marries Maggie and Sue marries Kent. They each have kids.
Because the kids don't have any differentces in there blood and have the same family on each side--unlike the usual set of cousins, which would normaly share one side but not the other--does that mean that they are very close to siblings? would it be closer to siblings if both sets of parrents were identical twins?

Answer 1

That's pretty strange, but possible. They would still be cousins, obviously, but the risk of diseases and birth defects would be extremely high, and this type of arrangement is not recommended, it is very bad to mix the bloodlines like this, the children will have mental and physical defects. It is really a very bad idea. And a very bad example of a hypothetical situation, I think I'm going to be ill.

Answer 2

Well, a brother and sister can be twins, but they can't be identical twins. Also, they still have different DNA.
If Max and Sue are cousins with Kent and Maggie, that means that both their dads are brothers with each other, or both their moms, or one of each, but each set of siblings still has some totally different DNA that they got from their other parents. Also, say their dads are brothers, even if they were identical twins the kids would be geting half their DNA from the mom. And what if Max and Sue had another brother? He has different DNA mixture from their parents then Max does. So if they marry their cousins then the kids they have will still all be different from each other. They will also share more similar DNA with their siblings than with their cousins.

P.S. even though there is a social stigma that goes with marrying cousins, there is nothing technically wrong and the risks of birth defects would NOT be "very high"...the risk would increase only if they kept marrying cousins and siblings for many, many generations. If two first cousins get married, probably their children with be totally healthy.