IAH Concierge/VIP Service for United Connecting Flight

My parents are flying from Sydney through IAH to Newark with a 90 minute connection. I am a little worried about them getting off the plane, clearing CBP, rechecking bags, transferring terminals, and re-clearing security in that timeframe.

I see United offers Signature Service and was wondering if anyone had any experience with it at IAH for an international connection.

Let me know your thoughts.