can ping out, but can not ping in

Greetings,
I am small WISP with 10 clients. My network is basicly made up of mikrotik routers.

Setup:
Office Router:
wlan1: 10.5.51.10
wlan2: 10.5.52.10
eth1: 192.168.0.254

Valley Router:
wlan1: 10.5.51.11
wlan2: 10.5.52.11
eth1: 192.168.4.1

Office Router and Valley Router connects wireless via wlan1 on both sides.
Clients connect via pppoe to wlan2 on both routers.
Client accounting is handeled by Userman
Clients who connect to my network all have a mikrotik router. they all receive IP’s in the range of 10.5.50.x
eth1 on office router connects to my office network and the internet.
eth1 on valley router has no connections on it as it is a remote router on top of a tower.

My Problem
from the valley router i am able to ping any client router on the network.
But from the office router i can only ping client routers connected to the office router.
I want to be able to ping all client routers connected to my network from my office.

please advise.

Here is a layout of my network to help explain my problem:

The situation I have is as follows:
• From “My PC” I am able to ping the Mikrotik RB411 in “Client 1” on 10.5.50.25
• From “My PC” I am NOT able to ping the Mikrotik RB411 in “Client 2” on 10.5.50.35
• From “Client 1 PC” I am able to ping “My PC” on 192.168.0.21
• From “Client 1 PC” I am NOT able to ping the Mikrotik RB411 in “Client 2” on 10.5.50.35
• From “Client 2 PC” I am able to ping “My PC” on 192.168.0.21
• From “Client 2 PC” I am able to ping the Mikrotik RB411 in “Client 1” on 10.5.50.25

I would like to be able to do the following:
• Have access to all my client Mikrotik Devices on my network to be able to provide remote support on their Router Boards.
• Be able to log in from the internet outside my network and have access to all my devices on the wireless network for support remotely from the internet if I happen to be away from office and out of town.
• Allow my clients to run applications like remote CCTV monitoring software where the application acts like a HTTP video streaming server and is accessible from the internet. Currently the application is not accessible from the internet, only on their local network.