Where should I arrange to meet the other runners?

You can organise with the other mission runners where to meet in advance of the task. Typically, if there is more than one person signed up to a mission, people agree to meet outside the property just before the task is due to start.

Please be aware that this may draw attention to the person's property and may signal that they are in some way vulnerable. So it may be preferable to agree to meet a short distance away and walk together to the property. Be vigilant for people around you while waiting and if anyone suspicious asks who you are then you can explain you are waiting for a friend/visiting a friend.