Members not receiving notifications

Started a channel.  Brought in 3 others.  Those 3 receive notifications (sound beep and a number on the icon) from other channels they are a part of.  However, they do not receive those when we post in our channel. 

Thus the problem has to be with my channel not notifying them of posts.

What do I need to look for, to ensure posts on my channel are causing notifications with other members?