Is this position legal?

Yes, I know that that that solution already exists, but I just want to be proud of myself for finding that myself before checking the forums!

Legal

#1581-Not legal as there are no missing black pieces to have made the white pawns on the e-file doubled.

#1579-Not legal as there is no black king on the board.

#1578-Easily legal. Here’s the quickest way that I found reach that position-moves.

King simultaneously checked by Bishop and Rook, no possible discovered/double check, both positions illegal.

Wrong

1587a is illegal, 1587b is legal.

#1590-Kapeesh kaposh, lemon squeezey easy! It can certainly go a few moves faster.

If blue to move then yes (blue would be in checkmate), otherwise I don't think so.

My bad, didnt see en passant. 

First pos illegal.

        Black king has to get to first rank before en passant. For an en passant to happen, Wpawn on b2 has to move to b4. With pawns on b2, c2, f2, and g2, BKing can't go to first rank.

Second pos legal. BPawn instead of Wpawn on c2, BKing can go to first rank.

illegal.

#1597-Illegal as there are no missing black pieces for the white pawns on the f-gile to have doubled up with.

#1599-Illegal, as it is impossible for that white bishop to have gotten to the white queen’s square without either the c2 or e2 pawns. As they have not moved in the position, it is illegal.

There’s also the fact that the g7 pawn has not moved either.