Ok,.....You know I think the world of you but here goes
You are still enabling their behavior (both MIL and H). He called K was asleep. Nothing more needed to be done. Lessons learned here my friend. It was not your job to text H to let him know K was awake nor was it your job to get MIL on the phone. Let them initiate or call back, that is their job if they want to do the right thing for daughter/grandaughter. You are way passed needing the be the nice guy here. If they want to talk or give bd wishes it is on them. I know it hurts your feelings for K that they didnt make her a priority but that is their deal. You just need to continue doing what you do and leave them on their own. Contact should only be what is absolutely necessary only. When MIL texted you in the morning I would have just texted back with a quick to call K when she had the time. Put it right back on her. Not your job to do this for her.
These people are amazing. Truly. I guess none of them including your inlaws have consciouses (sp?) As a grandmother and mother I can tell you nothing would have prevented me from wishing my granddaugher a HB on her day especially not some slut my son was sleeping with.
You need to be good to yourself and concentrate on lettting them all go. Soon they will just be people that really have no meaning in your life other than K. Soon.