what rights do i have as a half sibling

[eviesmith]

my brother is one and a half and me my dad and sister have not seen him since july 2020. he lives with his mother who has two other kids one of which does not live with her due to her cocaine addiction, my brother was born addicted to cocaine. social services are involved as my dad and i had both contacted them prior to his birth. the mother has made claims of my dad being abusive however consistaintly invited him to her house during the period of time she stopped us seeing my brother. my dad showed the messages proving this to social services and still we have had no luck. social services also will not talk to me or my sister or any of my dads family but do talk to my brothers mothers kids and parents. if anyone can help or give any advice at all that would be apprectiated so much , thank you in advance.