You can use the Ecobee Suite Smart Mode/Routine/Program Helper to manage and control what happens. In the described case, you would create a Smart M/R/P Helper that watches the SmartThings Routine that you have run when everyone leaves (Goodbye!), and set the thermostat to Away; and another watching the ST Routine that runs when anyone returns (I’m Back!) to set the thermostat(s) to Home.
That helper will change the thermostat’s Program if it isn’t already what is desired, and it will use the hold type you specify (permanent or temporary/until next change). Basically, temporary will put the thermostat back in control of its schedule, while permanent will put SmartThings in control of program changes. If you use the Smart Recovery feature of the Ecobee, then you probably want to use temporary.
You may also want to override the scheduled “Away” if someone actually stays at home (e.g., a sick or work-from-home day). I use another SmartApp to override the scheduled change to Away when I’m at home - I’ll probably add that to the Suite soon as another Helper - meanwhile, let me know if you need it.