My guess (we don’t have investigative reporting much anymore, so I don’t know) is that these NGOs are training “migrants” to lie on applications so they can claim to be escaping persecution (asylum claim). That would make them legally migrants until their cases are heard. So I suppose invader is more accurate than illegal alien. The illegals would be all those sneaking across.
Any illegal “migrant” or “alien” is an INVADER. Just like an invading army which is exactly what this is.