Wrong driver or Wrong setup? 2 x 1050 Ti

Hello there!
This is long story. So, I got to this local PC store that I buy parts from, regularly. When I got there someone wanted a 8 core CPU, so he went for like 8320E in Gigabyte 970 Gaming motherboard (non SLI). And looked like he went for 1050 Ti from Zotac. I stayed there for quite sometime. The PC builders normally build medium end builds or lower ones. So, the customer who wanted that build came again to shop and see if the build is finished. I was upstairs at that time. He said he wanted two GPUs for that setup. I was still not there. He then billed it. The store didn’t have return policy. When I came down stairs couple of conversation were going on about the GPU compatibility in that motherboard. I said, the board is not SLI compatible even if it does 1050 Ti is not SLI enabled. So, it’ll work fine with single monitors from each GPUs. So, then they went ahead and installed it. The board detected it and booted normally. But the drivers wouldn’t install. Says some kind of driver not compatible with the OS. They installed W10 Creators Update x64. Driver was download fresh off of website. It was 390.65. I don’t know why it was showing that error. I tried old ones. Still doesn’t work. I’m pretty sure I downloaded the drivers correctly. I have over 10 years of experience in this field. Device manager said the something like device wouldn’t start because of no drivers or something like that. So, I thought, it was driver problem. But, got output from both monitors with “Microsoft Basic Display Adapter”. I help them quite a bit here and there. So, I was stumbled upon that I couldn’t solve it. I have no idea what the problem is. The system is still in the shop and today the shop is closed because of Sunday. Tomorrow I’ll have to go there to solve it. Also, if you’re asking why he didn’t went for 1060 and all. It was not my choice or I wasn’t there when their customer was getting quote from the sales manager. Sales manager was not that good in selecting components. So, please strike off all your thoughts or components selection and all and get to the technical stuff. WHY IT ISN’T WORKING? WHY DRIVERS ARE NOT INSTALLING? I’m pretty sure I’ve seen people using two GPUs in same system without SLI bridge or no SLI support in same system got installed the drivers perfectly. Please let me know.

TL;DR 2x1050 Ti in Gigabyte 970 Gaming Motherboard, correct drivers aren’t installing. Showing errors OS not compatible or something like that. But they’re the correct drivers.

Thanks :)