Good enough for my Grand dad, good enought for the this rabble: first thing quarantine them and check for disease and criminal behavior or “moral deviance”. Find a sponsor who will ensure they do not become a burden to society and who will provide for their well being or assist with same if they can find a job. Release them as lawful immigrants with the previso they will not be on public assistance or welfare of any kind. Make them register every year as to where they are and send them an update card to that affect. If they don’t register or if they lie, send out a deportation official, lock em up, process them quickly and send them off to their native land PRONTO. Any costs for any of this go to their sponsor or sponsoring organization. Gone in 60 days start to finish at little cost to the tax payers.
As far as temporary holding goes, I recall doing my basic in 68 in barracks that had been condemned in 45. I am sure there are such facilities about now, perhaps not condemned in 45 but perhaps in the 70s. Good enough for me, good enough for them.
What you just wrote is Amnesty
Deport them all....otherwise its Amnesty