Accessing ftp server through another router

[xikes]

Hello.
I'm a bit new and inexperienced with all things networking.
I wanted to set-up an FTP server and have it be accessed from various devices in my network.
I'm having trouble with accessing the FTP server through 2 routers.
To illustrate, my network looks something like this:


In this diagram:
FTP server is set-up and running on PC1.
After tweaking some FW and port forwarding rules I managed to gain access to the FTP server from PC2, PC3 and Phone1.
But I'm having trouble with access from PC4, PC5 and Phone2.
What would need to be done in order to access FTP server from Router2's devices?
I tried some port forwarding but was unsuccessful and also for this case I'm having trouble understanding what needs to forwarded to where.

Some trivia:
Router 1 is a generic ISP router with WIFI (Alcatel I-240W-A)
Router 2 is a different router with WIFI (Huawei WA8021V5)
Why use two. Because Router1 is the one that's connected to the internet, but only has 2,4GHz wifi.
But Router2 has 5GHz wifi.
They both came from my ISP and (I assume) to some extent, are configured remotely/automatically, because internet access worked out-the-of-box.
That said, I have access to settings for both and can change various things like port-forwarding, DDNS, wifi ssids, etc.

Any help/tips would be appreciated.

 

[JogerJ]

Router 2 should act as an access point (bridge mode) and not connect as WAN, otherwise devices connected to router 2 will have a separate NAT layer below router 1 and thus devices cannot directly communicate between the two. Huawei ONT Bridge Mode might help