Scripts

then you can add before MoveHeroRealTime

ChangeHeroStats("Hero3", 7, 3500);

in general, I advise you to take a look at how it is done in the developers' campaigns, in the 1st mission of the Fortress, if I'm not mistaken, Laslo follows Frida... They made an in-script function to check the distance, so the heroes constantly stay close to each other.