If the leader is doing it from Realm Connect App on an iphone, at the bottom of her screen when she logs in, there should be an option at the top with pencil next to the word 'post'. Click on that and choose the group she wants to send the message to. It should open a screen to begin typing her message. There is a choice at the bottom that can be clicked indicating if replies are accepted or not. As long as everyone in the group has an email address, members will see the email both on their Realm Connect app as well as in their email box. If they respond in Realm, all members will see the response.
When our church started using Realm, I chose a person that had the access a regular congregation member, trained her on some of these type problems and see how they appeared on her phone. It really helped because she could then assist others with problems - she saw what they saw.