If you are using the macro
KissAssist to help with heals, one problem you will have is the
kissassist macro automatically loads and uses the functions of the plugin
MQ2Melee. The plugin will attempt to automate the combat functions of the tank. This is the primary reason I do not use the macro
kissassist. I do not think there is a way to run
kissassist without the plugin. Look at one of the healing only macros for your healer and make sure the plugin
MQ2Melee is disabled, =0 in your macroquest.ini file. Check out the thread
http://www.redguides.com/community/showthread.php/34604-Fast-Heal-6-Initial-Release-9-2-2015 for one of the many healing macros.
Your other option is to run
kissassist on both toons and set up the tank so
kissassist does as little as possible. See the guides for using
kissassist.
Just so everyone knows I use my own custom macros that are written specifically for my group and style of play. My group usually consists of a warrior (tank), monk (puller/dps), druid (dps/healer) and at least one healer merc. The other slots in the group vary depending on my mood that day, other mercs, mage, shammy, chanter, or extra dps from an additional warrior or monk.
MQ2 by itself does almost nothing. It is the various plugins and macros that make things happen. I know each character can run different macros even on the same computer, not so sure about having different plugins loaded... Hey developers that might be an awesome feature, load different plugins for different characters on the same computer.