Selecting 36V, 12V and 9V from 3 different PSUs
Exactly as @Jasen says, naive application of drain-coupled P-MOSFETS will give you a nasty surprise. When 9V is active, the FETs for 12V and 36V will still see their diode reverse-biased so all is well. When 12V or 36V are active, all voltages below will see their diode forward biased and two or more FETs will fight over control of the voltage. Whichever one loses will probably release its magic smoke.
Consider instead PNP BJTs. The critical parameters to look for are

Max Ic &gt; 300mA
Max Vce breakdown &gt; 36V
Low Vce sat

You have not specified how much voltage drop between the supply and the load you can tolerate, but 500mV Vcesat is frequent, 200mV possible (depending on how much you want to spend). Consider the PBSS5540Z with

Ic &gt; -5A
Vce &gt;= -40V
Rcesat ~ 55mohm, for a loss of ~17mV at 300mA

You have not shown what drives your MNB and MF1-2 signals. You'll probably need low-side, open-drain-style switching to appropriately bias your PNPs.



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