Lead DBS (non-group normal mode) supports multiple leads since the recent release (with limitations). But if it’s just for visualization, this should work. You’d need to switch the “3” and “4” togglebuttons on and localize them again (or manually merge the two ea_reconstruction files in your separate folders in Matlab).
That should make it possible to look at them in native space.
As you probably know, lead group only works in MNI space (given it’s designed for group analyses).
Hope this helps!