I know you can signal the flashes with the built in flash on the Nikon D750, but I was wondering if there is any other options, I hate to blind my clients with the built in flash all the time!
I'm kind of confused by your question. The YN-568EXII is Canon-only. There is no Nikon version. And e-TTL is Canon's flavor of TTL. The Nikon version is i-TTL. If you're trying to shoot with Yongnuo's for-Canon gear with a Nikon camera, you cannot get TTL or HSS on the hotshoe or on radio triggers. You can only get TTL and HSS through CLS (Nikon's "smart" optical slaving system). The TTL and HSS communication protocols are proprietary and brand-specific, and you'd need to use the YN-568EX for Nikon (it will have gold lettering on it, not silver). The Canon gear only gives you eTTL and HSS with a Canon camera and Yongnuo's 622C triggers.
If you are shooting with a D750, you need the Yongnuo 622N triggers (or other iTTL-capable triggers) and the for-Nikon Yongnuo YN-568EXs (Mark I) to maintain iTTL and Auto FP (HSS) communication.
Use a Yongnuo 622N-TX transmitter on the hot shoe of your camera and a Yongnuo 622N trigger on each of the 568 EX II N flashes. You can also buy them together in various combinations of 622N-TX and 622N units. You could use a 622N for the transmitter, but the settings are nowhere near as intuitive with the 622N (no screen, just status lights) as with the 622N-TX with an LCD screen. And the 622N-TX is not really any more expensive than a 622N, it just loses the ability to be a receiver in exchange for the LCD screen.