For M: Carbon 1 has the aldehyde; carbon 2 has the methyl group. Carbon 1 priorities: 1) C-Br 2) C-C/Br/CH3 3) C-CHO - I get an S; carbon 2 priorities: 1) C-Br 2) C-C/Br/CHO 3) C-CH3 - I get an S (it looks R but the H is in front so reverse to S).
For N: same priorities as M. Carbon 1 is R; and carbon 2 is R.
For O: same priorities as M. Carbon 1 is R; and carbon 2 is S.
For P: same priorities as M. Carbon 1 is R; and carbon 2 is R.
I think where you're making the mistake is that you're making the aldehyde the second priority and the C-C-Br group third priority; however, the C-C-Br group is second priority. Think of playing the card game war.
I have an A, you have an A. Go to the next card. I have a Q, you have a K. I win. Does this help?