Family analysis in PLINK

Question

[Jacob]

Hello, I am trying to perform a a family based analysis using --tdt. My .ped file does not include an FID so I am planning to use --update-ids and --update-parents to include the FID and sire/dam information. However, I have families where the sire is a member of multiple families. For example:

FID IID Paternal_ID Maternal_ID

0 10 20 51

1 11 20 52

2 12 21 53

3 13 21 54

My question is how do I update the FID of the sires if they are members of multiple families?

Thanks