The Xiaomi Redmi 6 and the Redmi 6A are the successors to the budget Xiaomi Redmi 5 and the entry-level Redmi 5A respectively. The Mi 5, on the other hand, is a 2016 Xiaomi flagship. Instructions on how to flash a MIUI 10 China Developer ROM are available here.
The unofficial Xiaomi EU project has also released MIUI 10 ROMs for all three devices. Xiaomi EU is based on MIUI China Developer ROM, and includes Google Play apps and services by default. It also includes more languages than the official version of the China Developer ROM. The Xiaomi EU unofficial MIUI 10 ROMs for the Mi 5, Redmi 6, and Redmi 6A can be downloaded here. Instructions to flash the ROM can be viewed here.
Xiaomi has stated that more of the company’s devices will start to receive MIUI 10 China Beta and MIUI 10 Global Beta ROMs starting this month. MIUI 10 adds portrait mode for single-camera devices, a redesigned user interface with a new Recents menu, and other “AI” features, which means that it’s a significant update for Xiaomi devices.