What is the general usage of "among others"? In my current understanding, I would say it is similar to "and so forth".
Check this definition among others:
. used to indicate that there are several more people like the one or ones mentioned, but that you do not intend to mention them all
He is expected to be supported at the meeting by Dennis Skinner and Tony Benn among others.
The gallery has an excellent collection of Impressionist works by, among others, Manet and Renoir.
This is different from and so forth, which only refers to similar things that are not identified. In contrast, among others refers to unmentioned items in a finite group.
I think the OP's confusion is not wrong because the phrases "among others" and "and so forth" are defined in different words in different dictionaries. Some definitions of these phrases seem so much alike. I think Macmillan has defined them in a very simple and clear way, which are as follows:
The phrase "among others" is used when you are mentioning one or more than one person out of a larger number.
The phrase "and so forth" is a synonym of etc. It's used after a list of things to mean "and other things of this type".
The phrase "among others" can be used in the beginning, in the middle or at the end of a sentence, such as "Among others, Adam and Smith supported me at the meeting, Adam and Smith, among others, supported me at the meeting or I was supported at the meeting by Adam and Smith, among others.
On the other hand, the phrase "and so forth" is usually used at the end of a sentence, such as people don't favour the Government's policies on health, education, tax, and so forth.