Looking for 1/2 Brothers and sister all adopted, Mother Kerri Hughes, Welsh

Hey, My name is John P Bolton aged 23yrs, DOB 06.12.1979, and I am looking for any information on my half brothers (2 but could be more) and Half sister, and mother. The children who have all been adopted in New Zealand. All of the children know that they have two half brothers in the UK. I believe there maybe another child, Bernard Jacob Van der Merwe.. I have a full brother, Carl Simon Bolton and another half brother, Daniel Stephen Bolton all living in Manchester, Uk. Our Mother is Kerry Yvonne Hughes, DOB being 7/2/59, and she is originally from Pwhelli in Wales, Great Britain. Unfortunately I have very little information as the family in the UK is very much divided. I have never met anybody from my mothers family even though I am originally from Manchester, uk, just a couple of hours from them. There are lots of questions I need answering, as I am sure most people on the site do. I do have a passport number and citizens reference number for her, where do I go from here? I know this is a long shot but I must start somewhere... Good Luck to all and God Bless Regards, John P Bolton :)