Dear Kimberly,
Yes, the child has legal rights to inherit property of his father (your husband).
The law presumes that he acknowledged parental responsibility by catering for his basic needs – paying fees, offering food, medication and shelter – for nine consecutive years.
Legally, a man acquires parental responsibility over a child who is not biologically his by living under one roof with the mother for 12 months and providing basics of life over the period.
Moreover, your husband never divorced you despite your adultery, a major ground for divorce.
As for your second concern, you have legal options should your husband make good his incessant threats and leave your son out of his will.
You can move to court and contest the will arguing that the father left out of his estate a child who was also his dependant.
The court would issue orders that the child be included in the estate as a legal heir and even direct the exact portion of his share.
Moreover, it would also not be a crime should the biological father of the child also give the child a portion of his investment as a gift.