in season 1 there two witchs called Barth & Mary how come they never seen again?

I don't know. :( Of course, Reta Shaw (Bertha) came back to the show several times as Hagatha and other characters.

They probably turned out to be Hagatha and Enchantra.

I'm sure the writers decided to simply turn the characters into more aunts for Samantha like comedyfreak suggested.

It's too bad Madge Blake never returned to Bewitched. I also enjoyed her as Larry Mondello's mother on Leave it to Beaver.