Problems when your spouse has a child from previous marriage.

My spouse has a 8 year old boy from his previous marriage. Custody is rightfully his however his ex wife takes him half of the time. I don’t think it’s possible for me to have much connection nor bond with him. As he’s always mentioning his mother or on the phone with his mother. At most I will be a friend of his once we live in the same household. I am expecting a boy too, week 18 now. Should I be worried about assets if I die , half of it goes to my biological son. However another half goes to my spouse. Who will eventually split with his other son if anything happens to him, and by law his son who is not my son, does get 50% of his assets (bearing in mind a portion is from me if I die first). Will like suggestion on this. Anyone in the same situation? How do you handle this? My assets do make up a good amount .