Does that mean that only the same function can be run multiples times in parallel as in the provided example? Or it is possibly somehow to force it to call two different functions?
You just leave it auto (default when there are tools) and let it decide. Are you trying to get it to call the same function, or different functions? From my tests it will call the same function in parallel but not different functions. To get it to call another function you have to pass the results of the first back in.