Find Ancestors

I previously put a message out trying to find my half brother and sister from my fathers second marriage.I now have some news to tell them regarding there biological father and have recently used a tracing service which reveled that my half brother has changed his name? proberbly was double barrelled when his mother re-married.My half sister is called susan lorna williams(maiden) born in 1970 in chester.My half brother is kenneth gordon williams at birth also born in chester in 1971.I am the eldest child from there biological fathers first marrige and it is urgent i find them(hence the tracing service) There mother is/was a lorna june earley from mold north-wales and there father was kenneth gordon williams also from mold north-wales.Married late 60's and lived in chester untill about 1972 when there mother left with my brother and sister to the bristol area.As my brother is believed to have changed his name it is very difficult where to go from here? If any of these details ring a bell please get back to me.I believe susan ended up in london working according to our aunties denise and yvonne.Any help appreciated.