I have two separate circuits containing nmos, i need to gnd the body of nmos of one circuit and give different negative voltage to the body of nmos of the other circuit. Is it possible to draw the layout of both devices in a single mag file.

You can, negative body NMOS transistors need to be inside an insulated p-well pocket, by using a nwell ring and a deep nwell

Does a double-well example design for sky130 already exist somewhere in the open?