I have a sensitive green horse at a private barn with a lot of know-it-alls, and most of the other horses are very chill and older. I don’t let people distract me when I’m working with him - I just say “I’m sorry, I have to focus on my horse” and ignore them. If you need them to move because they’ve come over to physically “help,” say “He’s pretty nervous, can you give us some space?” He doesn’t have to be nervous… if he seems at all alert/animated they will probably take you at your word.
If they’re really friends, I might later say, “Hey, I appreciate you looking out for me, I know Dobbin can be a lot, but I need to have all my attention on him when we’re working. I have a trainer/have a plan/have lots of experience with this, but if I need your help I’ll ask.” Instead of chastising them, make it about YOU and what you need so they still feel ‘helpful.’
As someone currently in the middle of this, I will also say it’s important to make sure you are staying clear-eyed about the situation. You don’t want to get defensive and then dismiss true behavioral problems or pain as normal green horse stuff. You also don’t want them convincing you that your horse IS behaving in a concerning way if he isn’t. Do you have other horsey friends, a trainer, or an outside support system that can provide another opinion? I am actually moving my horse to a barn with a trainer who focuses on green horses and restarting OTTBs because I want to be around people with a similar philosophy to me, who are doing what I am doing, and who I trust CAN help me when I need it. I was getting so much questionable “advice,” pushback and judgement over what I felt were pretty normal aspects of bringing along a green horse that it was starting to make me feel crazy.