The return of Williams comes 12 years after he left for a professional career that encompassed playing spells with Cardiff and Northampton and he previously coached Coventry who are in Neath's group in the new British & Irish Cup.
Davies coached locally at Bryncoch last season and made an instant impression with the Neath village club who were runaway winners of Division 4 South-West of the SWALEC leagues. Like Williams, Davies was first capped from Neath and he went on to play professionally at Cardiff, Bristol, Llanelli and The Ospreys.
Horgan said, "It is great to have the opportunity to work with three enthusiastic, young coaches who between them possess a wealth of experience at the top end of the game. All are bang up to date with modern methods and it promises to be an exciting time for Neath rugby."
Greeting the appointments, Neath chairman Geraint Hawkes said, "We are delighted to welcome aboard three aspiring, high quality, young coaches who have a lot to offer Neath and Welsh rugby in general. Both Steve and Kevin have just come from fully professional environments and this will add to the intensity and discipline the squad will need to drive the team forward in the new cross boarder competition."
Williams said: "Neath has always been my club even throughout my travels and it is a real honour as well as an opportunity to coach my home town club. Having been brought up in the locality and lived here most of my life, I am well aware of Neath's tradition and will do my utmost to continue and build upon recent successes."
Davies added: "I thoroughly enjoyed coaching Bryncoch last season and it is wonderful to have the chance to step up to Neath. I know how much rugby means to the town and the fans were always great to me. As a school kid I used to come to The Gnoll to see my heroes play and now I am looking forward to bringing on the modern day Neath heroes."
Morgan said: "After leaving the Dragons, I was looking for a position as a fitness coach and outside the regions there is nothing bigger than Neath who have really set the standards for other clubs in Wales. Neath have always prided themselves on their fitness and this is one area we must improve upon with bigger challenges than ever ahead of us. If needed, I intend to continue playing and it will be a real honour to become a Welsh All Black."