can they fit ?
if so do you need to make some sort of mount ?

 

I thought 5g civics had 6.5" stock.

 

6.5s will fit in the 5th gen Civics, with some modification depending on the type of speakers you choose. Usually you can just get away with cutting out the back of that speaker mounting basket already in the doors.

You might be required to make new trim rings to mount the 6.5s to the doors. However they will still fit behind the factory door panels. If you really want to get crazy (like me) you can even fit 8" Dynaudios into each door behind factory panels with clearance and power windows functioning. Its all up to the depth of the speaker and clearance you need.