i know of a few families who have a few girls lined up. i think that if they are relatively young, meaning they just came back from sem, and a girl a year or 2 older and than maybe one even older, they should wait. It’s incredibly painful to watch a younger sibling get married , (especially if its both girls/boys, i don’t think the issue is when they are different genders.) Once the girls are getting older, i think they should start dating. I know of a story where the parents started looking for the younger one , and b”h the older one got engaged first anyway.
i know of a different situation, where the parents were “extremely ” makpid on not skipping. They had a set of identical twins who were soooo alike in every way. There’s no way to know which one should go first, the only way to do it was, the oldest (it’s twins, so by like 10 minutes?!)