Just start your horses with you around to keep an eye on them. Keep the Highline higher than their heads, so they easily walk underneth it. Tie their leads short so they can't get a leg over the lead if the try and scratch their chin. The old standard rule is 7' high, 7' aprart and 17" of lead.
I do on occassions tie the leads a little longer so they can get their nose down to the ground to eat. I usually do this when I am around to watch, If left unattended, I tie themback up short.
Any water buckets I left around highlines usually get kicked over and horses get their feet tangled in the bucket, So I bring water and offer and then remove the bucket after they have drank.
I do get tired of wasted hay or pellets. So I place most of the feed in plastic Tubs and place it under the nose. When they are done eating I can drag the tub out of reach.
We've done lots of camping over the years, Early on, we would pack one horse and hike in leading that horse. As we got more horses, bigger trailers, I started packing one horse for 2-3 people. I'm a big enough guy that I don't want to add extra weight to my saddle mount. I just never carry more than what I can fit into my saddle bags and coat tied behind the cantle. Although I've seen friends put their lighter kids on horses and load pack gear on with them.
I often hunt off my horses. When I shoot an elk, we carry panniers behind the cantle and get off load the panniers and lead the horse back to camp.
My daughters have enjoyed many a camp out with their dad, leading an extra horse across the mountains