Clip on both sides instead of one?
No. Only clip ONE wing.
If you clip both, it will handicap them some, but they can just flap faster/harder and still fly.
Clipping ONE makes them lop-sided when they try to fly.
Kind of like trying to run if one leg was a foot shorter than the other.
You can probably clip back further...they don't really need to fly unless you have predator problems.