Practical way to park many bicycles in one garage for everyday use?
You don't say what other uses you have for the garage, but lets presume the floor space is a premium, otherwise a row of bikes racks is the obvious, cheap and best solution. 7 bikes will fit into 5 meters, and stick out about 2 leaving plenty of space . 

But you have 3.5 meters high, use it.... Rope pulley from the roof for as many bikes as you need to free up floor space.  These bikes would probably be less used ones. One or two bike stacker might be worth looking at e.g.


A wall hanging system such as  
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I would look at floor mounting for daily used bikes and hang/suspend from ceiling ones used less often. One thing I would say is get it sorted - theres nothing worse than trying to get out for a ride and having to move a million bikes before you get to the one you want.  With kids, having a place for their bikes gives you a valid reason to 'tell them off' when you trip over a bike left lying around randomly at the door way. While you at it, have a place to store helmets, gloves, pumps, car racks etc that is easy to access and setup so each item has its place. Once you have a place for everything, everything will be in its its place. 

The other thing I would say (from experience), is don't procrastinate, over think it and try to get it perfect first time, do something, if it does not work well, change it.