I'm not sure but if your EVGA PSU comes with 8 PIN to 2x 6+2 PIN PCI-E power cables then you should be able to connect both power ports on your GPU's using one single cable
The risers will connect to the peripheral/SATA ports on your PSU using either molex or sata cables, try to avoid connecting more than one riser per power cable
I will be more concerned about your PSU's as they don't seem to be properly sized for your rig, the Zotac 1080 TI uses 180W at 100% TDP so your PSU's will clearly not handle your rig at 100% TDP so you should only be able to run it a lower power limit
Hmmm 8 risers and each psu only has 3 sata and 1 peripheral ports. I'm gonna be one short for the SSD.
I thought the 1070 ti's use a lot less power than the 1080 ti's?