Each spouse is unique. I can't mere a person with himself.
Just in case, I tried. I get an error-
"The primary and the duplicate records can not be the same record."
I need to merge family objects.
It sounds like you have linked a couple to each other twice as spouses. This makes two families in RM. Then it sounds like you have linked some of the children to one of the families and other of the children to the other families. And maybe some of the children may be linked to both families.
Because the people are the same, you can't merge. And there is no deletion that you could do that would be a good solution. So you need to do some unlinking and relinking. I would pick one of the families that had the most children linked correctly as the one to keep. I would make it the current family and link in any additional children that need to be linked. Then go to the other family and first, unlink each child in turn from the parents in the other family, then unlink the two spouses in the other family from each other. That should fix it.