To trim the muzzle hairs, I've had good success with the horse muzzle shaver. There are a couple of different brands out there, I use these: http://www.valleyvet.com/ct_detail.html?pgguid=6bbed98b-965f-475b-84a4-8f451844536e

If your horses are scared of the clippers, there is a great Pareilli video on grooming that my friend used on 12 year-old that had never been clipped. In a nut shell, she took a battery powered massager and rubbed it all over the horses body and around the face and ears. SHe did this for several weeks and the horses loved the relaxing sensation not too mention he got used to the motor sound.

THen she took the clippers and rubbed it over his body and face and slowly proceded to clip his bridle path and muzzle - un-tied.

I use cordless clippers on my young horses and do the same concept as above. Ears are little touchier, but can be done with patience. One thing to note is that the cordless clippers tend to bind on really thick manes, so I use them mainly for bridle path and ear touch-ups.

I wonder if your hand would get sore using manual ones on several horses. :)

A boarder who sold their horse left a Whal cordless clipper at my barn. Works great except the battery is only good for maybe one good trim and then needs to be recharged. Its probably old and a new battery might be better, but works great when charged.

Its like this one  http://www.valleyvet.com/ct_detail.html?pgguid=2e87c446-7b6a-11d5-a192-00b0d0204ae5