In regards to an "LLC"- Can I subpoena Members & Managers to appear for trial to be questioned?

Absolutely. The answer to your question lies with the Florida Rules of Civil Procedure that are promulgated by the Florida Supreme Court. In short, an attorney of record OR the clerk of the court may issue a subpoena for trial. See Fla. R. Civ. Proc. Rule 1.410 (a) and (b). The link to the PDF file is below.

What you must do is contact the court clerk (either the clerk of the court where the suit is filed, or the District Clerk's Office in the county where the suit is filed) and explain that you are a pro se litigant who must have a subpoena issued for persons to testify at trial.

If you merely want to summon them to testify, you are likely required to give "reasonable" notice. If you require that they bring documents or material (which they must have possession, control or superior right of access to) you likely must give them at least 30 days notice and request that the subpoena be issued with a "duces tecum."

Hope this helps. Good luck with your case!

Assuming this is superior court and beyond the small-claims/informal hearing. . . it depends. Managers should not be a problem. As to non-managing members, you'll have to prove to the judge that their appearance as a witness will somehow be cogent to your case. The judge may ask for depositions instead or refuse to issue a subpoena.

you can request it, but the judge does not have to allow it, if you can not prove that thier evidence they will present will have a bearing on the trial.

You can't merely subpoena people just to harrass them. So they can hire an attorney to argue thier appearance and you will have to present evidence that they will or have evidence that is needed in your case.

u need to look that up in a law library, try university of florida site