You can't hold them against their will, sadly. This would constitute unlawful detainment. Have the GW # on speed dial and try to garner as much info as possible from them, WO putting yourself in a dangerous position. I'm not LEO, but I've dealt with numerous trespassers and meth addicts on my property in the past. SCN or Biggun4214 will be along shortly to advise you on your legal avenues to pursue.