If you want to have the rest of your group subject to rgmerc's control, while your beastlord is fully under your control without rgmercs you can type in the mq console window /dgge /Lua run rgmercs. Make sure your group roles are set appropriately beforehand.
You'll want to change certain settings if something isn't working as you'd expect it to. Don't be afraid to explore to become familiar with where settings are located within the ui. There are times where broadcasting a command is more convenient than going into each characters ui to make the adjustments. You can see common commands by typing /rgl help and even more commands by typing /rgl set show.
As an example, adjusting my groups camp radius. It might be tedious to go to each character window to find the setting within the ui and make the change. I find it much quicker to instead type in the mqconsole window /dgga /rgl set autocampradius 35 or whatever radius I want. An even better option is to make a social hotkey that you can quickly edit the radius number and click the button for that change to take effect.
There are exceptions to this where you're changing a setting, but it doesn't have much of an effect or doesn't resolve your issue. You just have to remember, it's still in beta and its functionality is still being worked on.
If you want you can write a bug report in the RGMercs Lua section and provide details about what you're experiencing so that it might help resolve the issue with future updates.