What's the name of the guitar chord that I accidentally found?

If you're playing the F#m shape as a full barre, it should sound the same (only lower) as playing an Em shape. To keep it simple, lets look at the notes if you fingered an Em shape (because only 2 strings change) The notes would be C A E G B D. If you plug them into a chord name generator, you come up with Cmaj13 or Am11.

Since you're playing the F#m shape 2 frets higher, you'd raise those chord names by a full step: Dmaj13 or Bm11.

Do you see how the process works? If you know the name of the open strings, you can count up the chromatic scale to find what every note is. Actually, if you're going to play in alternate tunings, you *should* learn the notes....just like you did on standard tuning. (you did, didn't you?) Once you know the notes you playing, you can figure out the names of the chords....either by chord theory, or looking them up in a chord name generator.

Chord Name Generator

First put on new strings, so you can have a good clean sound, then start learning scales, do them over and over, it will build up speed and dexterity, get a guitar case scale book, try and not get frustrated with the chords, they will seem impossible at first but you will get it, and if your brothers guitar is a cheap one, that might be part of the problem, sometimes cheap guitars have a larger gap between the neck and the strings. Just try and have fun with it, learn the basics then go to sheet music to learn songs. Good luck!