this is a great summary of the answer to your question:
for questions like this - which many different people may have the same question on
the HELP CENTER is a great tool (from which the above link came)
Hi, I noticed this question this morning (and I know it's a long time since you asked the question)..... but there is additional information that may help you. As well as being able to link children to different sets of parents, you can specify what the different types of relationships were.
Here is further information from the FS Help Centre that may help you: