Hello Zacharias, thanks for your help.
Here ist my "diagram":
Yes, the are 3 mikrotiks but i can edit only "Main" - Router 2 which is hap ac lite. I also think there is no need to edit conf on Router 1 or Router 3 because if i just place my old Fritzbox in place of Router 2 everything works. Here is some config from Router 2:
/interface bridge
add admin-mac=CC:2D:E0:FD:83:FA auto-mac=no comment=defconf name=bridge
/interface wireless
set [ find default-name=wlan1 ] band=2ghz-b/g/n channel-width=20/40mhz-XX distance=indoors frequency=auto \
installation=indoor mode=ap-bridge ssid=MikroTik-FD83FF wireless-protocol=802.11
set [ find default-name=wlan2 ] band=5ghz-a/n/ac channel-width=20/40/80mhz-XXXX distance=indoors frequency=auto \
installation=indoor mode=ap-bridge ssid=MikroTik-FD83FE wireless-protocol=802.11
/interface vlan
add interface=ether1 name=vlan7 vlan-id=7
/interface pppoe-client
add add-default-route=yes disabled=no interface=vlan7 name=o2-vdsl use-peer-dns=yes user=DSLXYZ@s93.bbi-o2.de
/interface list
add comment=defconf name=WAN
add comment=defconf name=LAN
/interface wireless security-profiles
set [ find default=yes ] supplicant-identity=MikroTik
/interface bridge port
add bridge=bridge comment=defconf interface=ether2
add bridge=bridge comment=defconf interface=ether3
add bridge=bridge comment=defconf interface=ether4
add bridge=bridge comment=defconf interface=ether5
add bridge=bridge comment=defconf interface=wlan1
add bridge=bridge comment=defconf interface=wlan2
/interface detect-internet
set detect-interface-list=all internet-interface-list=WAN lan-interface-list=LAN wan-interface-list=WAN
/interface list member
add comment=defconf interface=bridge list=LAN
add comment=defconf interface=ether1 list=WAN
/ip firewall filter
add action=accept chain=input comment="defconf: accept established,related,untracked" connection-state=established,related,untracked
add action=drop chain=input comment="defconf: drop invalid" connection-state=invalid
add action=accept chain=input comment="defconf: accept ICMP" protocol=icmp
add action=accept chain=input comment="defconf: accept to local loopback (for CAPsMAN)" dst-address=127.0.0.1
add action=drop chain=input comment="defconf: drop all not coming from LAN" in-interface-list=!LAN
add action=accept chain=forward comment="defconf: accept in ipsec policy" ipsec-policy=in,ipsec
add action=accept chain=forward comment="defconf: accept out ipsec policy" ipsec-policy=out,ipsec
add action=fasttrack-connection chain=forward comment="defconf: fasttrack" connection-state=established,related hw-offload=yes
add action=accept chain=forward comment="defconf: accept established,related, untracked" connection-state=\
established,related,untracked
add action=drop chain=forward comment="defconf: drop invalid" connection-state=invalid
add action=drop chain=forward comment="defconf: drop all from WAN not DSTNATed" connection-nat-state=!dstnat connection-state=new \
in-interface-list=WAN
/ip firewall nat
add action=masquerade chain=srcnat comment="defconf: masquerade" ipsec-policy=out,none out-interface-list=WAN
I guess i need some forward rule but i can't set as you suggested because L2TP is on Router 3. I have tried to set forward accept for in-interface ether4 and out-interface ether1 on Router 2 but it is red because ether4 is slave/bridged to ether2-5