Sometimes there are an missing profile between two known, the easy solution is just to create one and add a footnote, example: You have 1, misses 2, but know that 3 is the grandchild to 1.
Sometimes there are another problem, you have 1 and 2, but do not know if 1 are the father to 2 or vice versa, solution, add a footnote.
The idea that just leave them out just because you do not know the order are in my opinion totally wrong.
Yet another common problem are multiple parents, 1 was first married to 2, then to 3, but which mother are the mother to the child?
Solution, pick the most likely, and just add a footnote that the other one could be the mother. I have really hard to understand the ones that rather choose "unknown" as mother in this sort of cases.