Does anyone know if Benny has parents in the show, or if his Grandmother is his guardian?

I was completely wrong. Benny at least has a dad. The leaf-blower they use in "Three Geeks And A Demon" is his dad's (I think) and in "Smells Like Trouble," Benny says his dad is "back on the dating scene." Sorry for the misinformation. :)

i think he does because he mentioned his parents before but i don't know if there his guardian or not

I think that his grandma is his guardian?

No Bennys grandmother is not his guardian his dad is.