"If you have something you want to tell me because you think it will help me do my job better, email me and we'll speak in private in the conference room. Do not comment on my work or crtiticize me in public anymore.
My background is technical and I don't have a lot of experience in management, so take my advice with a grain of salt
but I agree with something like the above.
I feel that it's possible/likely that these folks aren't trying to be "helpful" they're just talking loudly in front of each other to show their authority. Like peacocks strutting and showing off their feathers. They want to sound knowledgeable and experienced and they might be used to putting the last person who was in your position down to make themselves feel better.
I'd nip that in the bud while still giving them their "I am contributing" good feeling. I'd announce that you no longer want verbal suggestions. But if they have something they want to tell you about something, they are free to email it to you.
Then, every day at a certain time, you can quickly scan these emails. If there's a gem with good wisdom, great, use it. The rest can get the "delete" button. That way, everyone gets their gripes out of their systems and feels heard. And you can quickly weed out the unnecessary, unhelpful stuff. AND people aren't dogpiling on you verbally in front of each other, wasting your time and disrespecting your authority.
After you've given that instruction, as each person pipes up verbally with "my opinion is..." you can interrupt them politely and say "please, write me a note or send it to me via email so I can gather all opinions on the subject together and go through them later."