So this might related to this and hence it's resurrection. I am trying to power a little network of teensy 3s using the method above.
Here is a "completed" product for reference
And schematic for reference

The VIN / AGND / BVAT are all tied together on the PCB with each their own net (maybe the problem)?
PIN 23 is linked on all the teensys without any resistors or anything but it isn't configured as an input or output pin so I thought it wasn't an issue.
I am powering the whole board and teensys with a 3.3v version of
www.adafruit.com/datasheets/tsr1.pdf
The arduino Due is being powered with the 9v version
The problem
around 90% of the time if I power the board, only the Due and ONE of the teensys (A on the board or the one on the bottom right) will fire up, leaving the other two teensys cold. this is a bad thing.
Sometimes I get lucky and the other teensys wake up and do their simple blink routine that I've programmed for now.
What I've Tried
Something very odd though... if I power (any single one of the teenys) via USB they will
100% of the time power up completely fine. If I then turn on the board power and unplug USB everything proceeds without issue.
I have tried connecting both and either of the 3.3v pins (on all of the teensys at the same time) just to see what would happen, basically the same results. Though sometimes it starts to look like it will be happy, it fails on the next power cycle.
I've measured voltage from the Teensys in both states of working and not working and I get a clean 3.28v on all of their 3.3v pins, even if their light is off.
I've measured mA and get 0.42mA from the 3.3v pins to ground on all the teenys in both states.
PLEASE PLEASE PLEASE PLEASE help :'( I'm running out of time. Thank you anyone that can help!!