route LAN client connection with internal VPN

hi all
i used rb750r2 for our company. first i described about our network design:

eth1: WAN with DHCP client can get ip from ADSL modem
eth2-eth5: connected together with bridge
SSTP server: pool address is 10.250.10.0/24
l2tp vpn client: connect to external vpn (expressvpn)
dhcp server: 192.168.88.0/24

i want to route all dhcp client to external vpn with l2tp vpn client. i will setup l2tp client and add prerouting mange with mark routing and then add route 0.0.0.0 with l2tp connection and specify routing mark. all dhcp client connection routing from external vpn to external network and work good.
i have some problems:

  1. when our managers connect to mikrotik from other way with sstp vpn can’t ping dhcp client.
  2. i can’t connected to mikrotik with winbox from external network with ip static.
    all above problem raised when l2tp vpn client is on. and when disabled it, all above problem is solved.

Best Regards
Ehsan Farahani Asil