Was realy hard to understant what do you want to do.
Why do you have on ether1 ether4 and wlan1 an ip from the same subnet as your modem.
What is 5.0/24 netmask anyway… modem subnet? if so 5.1 is not your modem ip? how do you connect to modem? dhcp? static ip?
I think you should start over and configure accees to adsl router, make sure your mikrotik can access internet. (try a ping to google.com from terminal)
Then for your network use a single ip with a single dhcp server on an ether port connected to your lan then bridge or set master interface on other ports.
if you realy need a setup like in your pictures try to set different ip subnets on every port. My bet is as i can see in your routes 10.10.5.0/24 present on ether1 wlan1 and 4 is your problem. But if you only need a simple setup make only one subnet for your lan.
pppoe1 is a different interface than ether1 as far as IP is concerned. The modem doesn’t have a gateway or static routes set, so when you try to access the modem from the LAN, the modem needs to see the source IP as one that it knows how to reach, which is why the new masquerade rule is necessary.