Relationships and IBD sharing expected value in plink

Question

[dirranrak]

Hi all,

1. I am working on a new dataset and test the relatedness of all individuals by using --genome flag in plink. Why in the result, all RT (relationships) are UNRELATED and the EZ (IBD sharing expected value) are Non Applicable (NA)? even Z0/Z1 plot show the real case.
2. How exactly we can know the best threshold for the filter that we are going to use with the data?

Thank you