Min Max Quad Sudoku

Fill the grid with the digits 1 to 9. Each row, column and 3x3-box will have exactly one of each digit. The red points in the near of crosses where four cells meet each other show that the cell with the red points is greater then the three other ones. The blue rings in the near of crosses where four cells meet each other show that the cell with the blue ring is smaller then the three other ones.

i play this sudoku variant with my friends,but after a hole afternoon discussion,we only find out five dight 9.

first in C8 only R9C8 can be 9,than R4C1=R5C5=R8C2=R7C6=9

in N4,find a pair{R5C3,R6C1}=12

we also find some messages,like 8 locked in C5 in N8.but it seem no use

how to continue?