Son of Common-Law

[Pedro0705]

Hello there! Me and my common-law wife are creating a profile for an Express Entry but got stuck in the question "Does Pedro have a relative who is a citizen or permanent resident of Canada?" My common-law wife is still a non-resident/non-PR of Canada but her son, who is 25 years old, is already a Permanent Resident of Canada. I am the principal applicant so my question: Is the son of my common-law wife can be considered as my RELATIVE? If yes, what document do I need to prepare to prove our relationship (me and my common-law wife's son). Hope someone can respond to this inquiry. Thank you so much!