I am confused about pawn promotion. If I promote two different pawns, can I promote them both to a queen?
Even all 8 of them, if you manage to get them to the opposite back rank. Let's look at the relevant part in the Laws of Chess:
3.7e When a player, having the move, plays a pawn to the rank furthest from its starting position, he must exchange that pawn as part of the same move for a new queen, rook, bishop or knight of the same colour on the intended square of arrival. This is called the square of ‘promotion’. The player's choice is not restricted to pieces that have been captured previously. This exchange of a pawn for another piece is called promotion, and the effect of the new piece is immediate.
The bold emphasis is my own and probably the important part for resolving your confusion.
Yes. There are even at least two tournament games that were drawn after each side Queened two pawns while their original Queens were still on the board, for a total of 3+3 Queens on the board simultaneously! See the "most queens" entry in https://timkr.home.xs4all.nl/records/records.htm.
To answer your question directly, yes, you can promote to a queen twice (or more) in the same game. Any pawn that makes it to the opposite side of the board can be promoted to a queen. To bring that point home, here is a game where at one point there were six queens on the board: