pptp will auth, mikrotik can ping local and remote address, pptp client can ping mikrotik but the LAN can't. Also I have a problem where if the mikrotik isn't a dhcp client of the adsl router then pptp passthrough doesn't seem to work

Have you conigured gateway on the router acting as pptp client?
Post configuration of your routers, specific to what you are asking so
you can get better help