IF IDENTICAL TWINS MARRY IDENTICAL TWINS HOW GENETICALLY SIMILAR WOULD THEIR CHILDREN BE?

Identical twins Brittany and Briana Deane first met identical twins Josh and Jeremy Salyers last August at The Twins Day Festival in Ohio. A year later, the couples had their weddings, together, wearing the same wedding outfits, at this year's Twin Day Festival. Their weddings were documented for a TLC special called "Twins Marry Twins," scheduled to air in 2019.

When identical twins reproduce with identical twins the resulting children are genetically indistinguishable from full siblings. Source: http://familypedia.wikia.com/wiki/Double_first_cousin

DOUBLE COUSINS

Double first cousins arise when two siblings reproduce with another set of siblings and the resulting children are related to each other through both parents' families. Double first cousins share both sets of grandparents in common and have double the degree of consanguinity than ordinary first cousins. Genetically they are as related as half-siblings. Their coefficient of coancestry is 1/8th or 0.125. While double first cousins have the same coefficient of coancestry (1/8) as half-siblings, they do have higher chances of sharing BOTH alleles (1/16 vs. 0) and lower chances of sharing one allele (3/8 vs. 1/2) with each other than half-siblings.

When identical twins reproduce with siblings the resulting children are more related than half-siblings but less related than full siblings.

Children of double first cousins are double second cousins.