Join 2 Subnets and Port forwarding

I have one adsl modem router , tp-link and one mikrotik 951 router.

192.168.1.1 is the ADSL modem router , where i have some 192.168.1.0/24 PC’s

I want to create an alternative subnet 192.168.50.0/24 , where i want to join these two networks.

Since now I have configured mikrotik as 192.168.50.1 (default gateway) to all PC ,
assigned a static IP 192.168.1.2/24 for the ethernet1 interface masquerade , and
static router to 0.0.0.0/24 to 192.168.1.1 GW.

Since now all computers 192.168.50.0/24 can surf.

How can the 192.168.1.0/24 computers to be able to watch and ping the 192.168.50.0/24
and also how can
I want to forward port 80 , from any incoming from WAN , to my web server on 192.168.50.2 .

How can I do also this ?