Verified answer

Actualy alomost same.

みな is Everybody original form

みなが is Everybody are fine ~

みなさん is Everybody + San ( Polite and friendly version)

Our Japanese does not use みな.

Almost Japanese are using みなさん.

みな and みなが are literalism using in novels.

Emperor is only using when he called to citizens in Jpn.

Generally we are not using みな and みなが.

みな means everyone. みなさん also means everyone but it is usually referring to a specific set of people rather than everyone in general. For example when you are addressing an audience during a speech. The "san" makes it more polite, in the same way that adding "san" to the end of someone's name does.

みなが "Ga" is a subject marker particle, it functions similarly but not identically to は

自分 means myself. I don't know the situation in which you encountered it, but it is used in some regional speech to mean "you" as well. At this juncture (judging your Japanese level from the type of question you are asking) I would suggest you understand that it means "myself" and don't worry about knowing how to use it just yet.