Pat - there is a specific tool for the ford pistons, but I don't recall the make. I've used the square multi tool myself with moderate success - it's not a very good fit, so small needle nose pliers are probably better. You do need to push in hard at first to get the threads to bite before turning clockwise. The added C clamp sounds a good idea for this. If they haven't been touched for a while, say 60,000m on the last set of pads, then I'd highly recommend clamping the hydraulic hose and removing the calipers to the bench, where you can apply more force. At that mileage anyway you want to replace the brake fluid and clean & lube the caliper pins (with brake grease or preferably some silicone compound). They also tend to sieze at high mileage if not maintained.
Doing a thorough job always pays off and don't forget the rear calipers have to be bled in the ABS fashion, you can't just pump the brake pedal - you need to switch on the ignition, allowing the accumulator to build pressure, push the pedal down once and then carefully release each bleed nipple for about 10 secs at a time and the fluid automatically flows. Beware of the high pressure that the fluid comes out & turn the ignition on & off each time you release fluid until all the air is gone. The Haynes manual has a very good write-up on this and is only around $16.