German tells Customs and Border Patrol that she intends to break the law when entering the country, freakout that you cant punish people for conspiring/attempting crime

Gosh it's not like their Instagram page is still public and you can see all the dates past present and future they had been in US doing paid work despite not ever having had a work visa.

And then the just swans up to the border tattooing equipment in hand expecting nothing to happen. They might as well have worn a giant sign saying GUTEN TAG I AM HIER TO COMMIT DER VISAFRAUDEN JA

They're being held in detention because the US is seeking a lifetime entry ban and that requires hauling the in front of a judge in immigration court. If they're being put in a solo holding cell it's mostly likely due to the behavior they themselves admit to.