The WLAN repeaters must be closer to each other, sometimes that doesn't work any better. But I might have a better idea. A WLAN mesh router. These sets consist of 2 - 3 devices and can be expanded as needed at low cost. The cheapest solution I could recommend is a Deco M4 from TP Link:
Tp-Link Deco M4 AC1200 Dualband WLAN Mesh 3-pack
The trick with this solution is that the WLAN of the LTE router is off and the WLAN mesh system takes over everything, DHCP server, LAN connections and the coverage is usually no longer a problem, you have WLAN reception everywhere. With each Deco device, there are also two Gbit Ethernet connections.