Good day,
Nice ones, but some of those are pretty fast solving, I have seen them in chesstempo
Well here are the answers to some.
13) mate in 3 white to move I believe: 1 Qf2-c5+ Kc6-d7(pawn blocks b7) 2 Qc5-d6+ Kd7-e8(rook blocks c8) 3 Qe7#
14) mate in 3 white to move I believe: 1 Qf5xRf8+ Kg8xQf8 2 Nf4-g6+(double check) Kf8-e8 or g8 3 Rf1-f8#
15) mate in 3 white to move I believe: 1 Re8-h8+ Kh7xRh8 2 Qh5xh6+(g7 pawn is pinned) Kh8-g8 3 Qh6xg7#
16) mate in 4 white to move I believe: 1 d5-d6 Ke6-e5 2 Ra8-e8+ Ke6-d5 3 Ba6-b7+ Kd5-c4 4 Rb1-b4#
17) mate in 4 white to move I believe: 1 Qc5-c6+ Ka6-a5 2 b2-b4+ Ka5xb4 3 Qc6-c5+ Kb4-a4 4 Bf3-d1#
18) mate in 4 white to move I believe: 1 Kh3-g4+ Kh6-g6(do not let move Kh7) 2 Kg4-f4+ Kg6-f6 3 e4-e5+ Kf6-e5 4 Nb3-c5#
19) mate in 4 white to move I believe: 1 Re3-e8+ Bd7xRe8 2 Re1xBe8+ Kc8-d7 3 Nd5-f6+ Kd7xd6 4 Bh6-f8# or Bh6-f4#
20) mate in 4 white to move I believe: I liked this mate: 1 Ne4-f6+ g7xNf6 2 Qb3-f8+ Kg8xQf8 3 Bc1-h6+ Kf8-g8 4 Re1-e8#
Taken time around 30 mins to write them down here too in that time

Have a nice day ^^