That would be true with some styles of clamp but not others. There are several different styles of clamps many of which would almost certainly have the clearance to be usable.
One version which I actually own, not only has a low clearance screw it is also a deep reach or a C-clamp style which gives even more clearance. Jorgensen "Pony" Deep Reach Pipe Clamp is the name of this style of clamp that you will find very useful. You supply your own threaded pipe or if you can find this clamp locally they will also sell and thread your pipe. There are cheaper prices but this link should work:
My first reaction is... that I thought that you would be operating the clamp since you are "helping" them, eh? I assumed that you are the one who is handy and will own the clamps. Besides that, if these invalids can't pick up a 12 inch clamp they they may need your help every time they open and close this window.
The ones you own may be reversible since many are and you were previously unaware of the feature. Just try removing the fixed part of the clamp and reverse it. You call the clamps "newer" but they are nothing of the sort.
Pipe clamps are a well established technology, I assure you. They do indeed have a mechanism which allows you to position the movable part of the clamp along the pipe so that if adjusted properly only a turn or two of the screw may be required to to do the job. If your wifey won't let you buy any clamps then give the job to her!!