Liora, mazel tov, and may you be zochim to build a B”NB together.
It is not that it is an inyan – it is just a simple fact that after many years of marriage, many couples DO begin to resemble each other. They begin to adopt each other’s mannerisms and facial expressions, which has a lot to do with the resemblance.
Yes, there ARE couples who actually do seem to look like siblings. Maybe facial features that they love in their family members might be unconsciously sought out in a partner. But it does not guarantee that the marriage will be perfect. I knew a couple where you would NEVER believe they were not brother and sister. Unfortunately, their marriage did not last.
In any case, it is of little real significance in the grand scheme of things, don’t you think?