Mikrotik supports the Ohm's Law "standard"
(e.g. Watts = Volts * Amps)
Re: precedence on INPUT power, multiple power source should be fine but it NOT be a "good idea" to mix voltages of the power supplies (but likely work). Now precedence on OUTPUT PoE is generally software controllable on most switches (via "PoE priority").
I think you need to lookup at the max power
consumption of the device & the max output power of the PoE port for the devices involved first. And finally you need to make sure the total of all ports power is within the limits of the PoE switch. Three things to check before using passive PoE (e.g. typically ~24V). The 802 at/af/etc standard (e.g. typically 48V) neogiciates all this, so it just won't turn on if the power requirements aren't met (but still has some limit on max power per port and capacity, which is what's used by standard to determine if power is allowed).
These are all in Mikrotik's spec pages for all of there devices... But doing the "power math" is kinda important with passive PoE, so that what determines whether is "good idea to PoE feed all ROS".
If we pick a small PoE switch for example, like the RB260GSP, that has a max of 1A output per port. And limit of 2A for all PoE output. The "watt output" is determined by the input voltage to the switch for passive PoE. Let's take your 26V supply, so max watts per port would be 26 watts (1A * 26V), with max of 52 watts (2A * 26V). You'd need to size the power supply to include the power needed by switch. (so for RB260GSP add 5W for it's own power, or 0.2 amps (200mA) at 26V).
For the CRS326 says max of 21 watts. And let's take your 26V supply. So if you used the 5.5/2.1mm jack without PoE, you'd need at least 0.8 amp (800mA) of power. Now the issue with PoE is there is loss over line, so while you may start with 26V, it voltage will drop over the line, so that same 26V from switch to router over ethernet will be lower at the end of the ethernet line. This depends on cable quality and length, so let pick it's 22V at the end of 100m run, now you'd need to start with a power supply of at least 1.0 amp (1000mA) at the starting switch. But this is why you see a
range listed on the acceptable voltage: voltage drops with cable length, so the device deals with voltage it's getting (as long as in range), thus starting at higher end of voltage supported at start is important.