Hello! I Agree with the others. Create a routine and stick to it. Put them down and leave. I have little ones here who use to cry for 30 minutes at a time and really stressed me out! After about a week of being consistent, they dont even let out a peep (one of them it took two weeks). it will get better!
Also continue to tell the parents as they should know its taking a bit for them to adjust.

Good luck!