If 2 voltage sources V1 and V2 are connected in parallel to each other, what is the voltage between the 2 extreme ends...???

this is only possible when some internal resistance is present

in that case 

V =[V1/R1 + V2/R2]/[(1/R1)+(1/R2)]

where R1 and R2 ARE THE INTERNAL RESITANCES OF VOLTAGE SOURCE V1 and V2 respectively