How to connect 2 thermostats and baseboard heaters on one breaker?
In the first junction box with the first thermostat, connect with wire nut black wire from panel, black wire to next junction box, short pigtail wire to thermostat. Connect with another wire nut red wire from panel, red wire to next junction box, red wire to first heater. Connect black wire to heater to other connection on thermostat. Connect ground wire from panel to junction box then to wire nut, with ground wire to second junction box and to heater.

In the second junction box with the second thermostat, connect black wire from first junction box to thermostat. Connect red wire from first junction box to red wire to second heater. Connect black wire to heater to other connection on thermostat.  Connect ground wire from first junction box to second junction box then to wire nut with ground wire to second heater.