Spitfire,
Not to be excessively rude or anything, but could you possibly put all of your little questions into one post? It clutters up the forum when you ask a zillion little posts, instead of just one big one.
Now I will attempt to demonstrate said method by answering all your questions in one post.
Ants in Cage:
As to your question, no..one ant can't harm your snake. However, more than that may. I'd try and find where the ant came in and eliminate the problem there. Cause if they're in with your snake, they're probably roaming around your house and kitchen as well.
Stunning Prey:
As many stated in your previous post, why switch to live when yours is already on frozen/thawed? Frozen/thawed is the safest food you can offer your snake, period. No chance to bite, or maim your snake and offers little chance to pass on parasites. If you only want to feed live for the "coolness" factor, I think some maturtity on your part is in order. Yes, snakes are amazing to watch eat, but it's a part of life, not a game as it is for humans. Treat it as a part of nature, not a sportsman's hunting trip.
But if you insist on feeding live, then yes, stunning prey is a better route. I just whack mine with a heavy wooden spoon in the head. Just use your common sense. Me? I feed pre-killed pinks and fuzzies. Anything larger and it's frozen/thawed.
Eating Without Constriction:
Many of my younger snakes don't constrict a pinkie mouse. They'll just grab it and start swallowing. However when most of them moved up to fuzzies, they started constricting every meal. Some of mine even constrict f/t food as well.
Cage Sharing:
As Cav stated, there are many views of thought on this. However the majority of us feel that snakes should never come in contact with one another unless for a quick picture or breeding encounter. To house more than one snake per viv is laziness in my opinion. If you feel the need to have more than one snake, then you should take the time and money and be responsible for the snake's health and well-being. Snakes are solitary creatures and being in close contact with another may cause stress, disease, and ultimately death.
The search function on this website is top-notch. Just input whatever you're curious about and chances are it's already been discussed multiple times and you're in for a good read. If you can't find it, then post to your hearts content.