Ok now everything is isolated, is working etcc..
BUT
Not the Netatmo Thermostat Relay and Weather Station 
I've added them again to HomeKit but nothing, so I searched on the Netatmo and I've found this https://helpcenter.netatmo.com/en-us/smart-thermostat/connection-wi-fi-radio/advanced-network-troubleshooting-guide
Please check if your router has any firewall / port filtering. If so:
- Open the 25050 port (TCP).
- Assign the Wi-Fi module a static IP with its Mac address.
Now I've done also it and the Thermostat and Station are now connected and I can control them via Netatmo app or website BUT not from HomeKit 
I don't know what's going on with Apple protocols but these issues are mind blowing!
Netatmo website/app
HomeKit
_hap._tcp PTR Netatmo\032Relay\032(2)._hap._tcp
Netatmo\032Relay\032(2)._hap._tcp SRV 0 0 5001 Netatmo\032Relay-2.local. ; Replace with unicast FQDN of target host
Netatmo\032Relay\032(2)._hap._tcp TXT "c#=9" "s#=1" "ff=1" "sf=0" "pv=1.1" "md=Netatmo Relay" "id=xx:xxxx:30:BF:3C" "na_tkn=cba8" "ci=2" "sh=LJ/KDg=="
_hap._tcp PTR Weather\032Station\032(2)._hap._tcp
Weather\032Station\032(2)._hap._tcp SRV 0 0 5001 Weather\032Station-8.local. ; Replace with unicast FQDN of target host
Weather\032Station\032(2)._hap._tcp TXT "c#=11" "s#=1" "ff=1" "sf=0" "pv=1.1" "md=Weather Station" "id= xx:xxxx:F7:45:43:B8" "na_tkn=806e72" "ci=2" "sh=PQgp5A=="
Edit: I solved the DHCP issue, I had to create a rule in order to reach the .5 subnet from the main LAN
config zone
option name 'lan_to_iot'
option input 'REJECT'
option output 'ACCEPT'
option forward 'REJECT'
list network 'lan'
config forwarding
option src 'lan_to_iot'
option dest 'iot'
Now the only issue that I can't solve, is the Netatmo devices that are not working with Home app, I opened a new thread: Netatmo HomeKit native devices, not able to update iOS Home app when isolated (but work online/using Netamo app)