This is similar to the question concerning Genesis 2:18–19, did God form the
animals before or after he created man? According to Genesis 1 it was
before, but in Genesis 2 it is indeterminate. Likewise this bringing forth
sons and daughters is indeterminate as to being being before or after the
birth of Seth. Most likely some before and some afterwards.
According to English usage, it sounds like afterwards for both. But that’s
because English is understood differently.