"We would have met them here."
Translation:We zouden hen hier hebben ontmoet.
You don't need the unconjugated form here but the voltooid deelwoord which is used when an action has been completed. For "ontmoeten" the voltooid deelwoord is "ontmoet". You can recognize the voltooid deelwoord form of most verbs by the "ge" prefix though.
For example: I have seen the movie - ik heb de film gezien.
If it were "we should have met them here", would it be "we zouden hen here moeten hebben ontmoeten"? I mean, should I use the infinitive form of 'ontmoeten'? Because in the sentence "I should not have paid" people are saying it should be "Ik zou niet moeten hebben betalen" and not "Ik zou niet moeten hebben betaald" as duolingo show as translation.