Try changing the code at collsions 1,2,1,1 to
collisions 1,2,1,1
collisions 2,1,1,1
While Not KeyDown(1)
MoveEntity v_sprite1,x1#,0.02,z1#
updateworld
MoveEntity v_sprite2,x2#,-0.02,z2#
updateworld
RenderWorld
Flip 1
Wend
collisions 1,2,1,1
collisions 2,1,1,1
While Not KeyDown(1)
MoveEntity v_sprite1,x1#,0.02,z1#
updateworld
MoveEntity v_sprite2,x2#,-0.02,z2#
updateworld
RenderWorld
Flip 1
Wend