I've moved the LNB2 output on the Tevii card to a non-power pass port on another splitter and now most things seem to be working. Except the Tevii tuners still don't always pick up anything on some transponders so I have to scan those transponders again manually and then it seems to work.
make sure you only have one thing supplying power to the lnb, in my case i have a freeview top box suppling power and a splitter going to my Tevii S480 card, yes the voltage with the lnb unplugged is the same voltage as you have, however i turn my lnb power off as the top box is powering.
I think the main problem is that the Tevii card and the two Nova S cards don't like each other. They both work great on their own but with them all connected I start to see issues with no signal or similar. I've tried all combinations of splitters with all ports power pass and one port power pass only but makes no difference.
Thinking I might sell the Tevii card and the two Nova S cards and get a quad DVB/S2 tuner.