For crossfire you need identical chipsets and ram. Cards can be different, vendors, brands, editions anything else, but a 570/8Gb needs to be paired with a 570/8Gb.
As stated, Crossfire is dead. It was dying years ago. Game devolpers really didn't put much effort into it in the first place as intel/nvidia were setting the standards for games and fps. With Windows 10, crossfire and sli was effectively guillotined, DX12 is native to Win10, and DX12 is multi-gpu based, not sli/crossfire based. With the advent of the more powerful single cards such as the 1080ti+, the need for high fps from multiple cards went further out the window.
Crossfire only showed modest success in a handful of games, but also showed just as many negative results...