Hey. Sorry to hear about your temp and crashing issues..
It does sound hardware related and not software though. I would suggest to strip it right back. I personally use PiMP OS, but that shouldn't matter for this testing.
Try booting it with just 1 gpu (not the 35w one) and 1 psu connected.
Try making sure you have either the standard Rom, or only PBE One-Click mod ONLY.
As rikuu said, ditch the undervolting for now. Tune later.
Try a little more conservative setting, maybe 1025 and 1900? I have some 4gb rx470's (Hynix mem), running only PBE1C, 1025, 2025, NO UNDERVOLT, and getting 28.2mh/s@52w on ETH.
If you try the above.. run it for a day or 2 to see temps and stability.. then add a card. Slowly slowly.. you'll get to the bottom of it.
When you do find the issue and your rig's running stable.. then you play a little with undervolting to maximise your return.
Best of luck.. happy mining!