Bandwidth distribution

I have a ZBT WG3526 router with the latest OpenWrt available. My only WAN connection is a 4G mobile with traffic unlimited yet speed being cut due to the carrier base station heavily used and overloaded by other mobile users in the area.
I need to have WAN traffic distributed as per the following:

  1. Maximum priority to a couple of devices in the static DHCP lease list.
  2. Lesser priority to other devices in the static DHCP lease list with individual bandwidth limits applied.
  3. Lest priority to all devices not in the list with a default bandwidth limit (say 100 kbps per client).
    I tried using luci-app-nft-qos package yet it lacks proper documentation (i.e. what is static vs dynamic limit?) and I couldn't get it working (it has "Limit enabled" checked by default but it doesn't apply traffic limitation).
    Am I missing something? Or maybe there is a more proper solution to my problem?