How can I bind pptp-server to a specific incoming interface?

What should I do if I want to up two different ( authentication service ) pptp-servers on the mikrotik

I couldn't force L2TP/IPsec to at least respond using the same source for the response. I eventually had to dedicate routers specifically to act as VPN gateways on a single public IP.

One partial solution is to use the shared PPTP server that listens on all ports and control what happens when a client connects based on the /ppp profile that is assigned to the /ppp secret. Not a great solution, but it might work for your application.

How can I bind pptp-server to a specific incoming interface?

What should I do if I want to up two different ( authentication service ) pptp-servers on the mikrotik

Use firewall to drop/allow connection only from specific interfaces.

As for your 2nd question, can you please be more clear?
What exactly do you want to achieve?

I have two ISP one on 1st port and second on 2d port
I want to achieve next goals

1. pptp server on the 1st interface with a radius
2 pptp server on the 2d port with a different radius

At the moment both authentication methods work on both ports at the same time.

Also I want to achieve that a first radius server will response only on 1st interface and the same for second

I have two ISP one on 1st port and second on 2d port
I want to achieve next goals

1. pptp server on the 1st interface with a radius
2 pptp server on the 2d port with a different radius

At the moment both authentication methods work on both ports at the same time.

Also I want to achieve that a first radius server will response only on 1st interface and the same for second