1 Answer
imo, these character are in non-stardand small script; my best guess:
the bottom right is "春" (u+6625)
http://humanum.arts.cuhk.edu.hk/Lexis/lexi-mf/search.php?word=春
top left is "堂" (u+5802)
http://humanum.arts.cuhk.edu.hk/Lexis/lexi-mf/search.php?word=堂
bottom left is "製" (u+88fd)
http://humanum.arts.cuhk.edu.hk/Lexis/lexi-mf/search.php?word=製
top right character, not yet recognised :(