Laptop to control robot

As was stated before, you can't control a motor's speed with a relay board. I suggest a dual motor controller (H-bridge) with a serial interface. You can then command the motors' speed via serial port commands.

BRW

Your post indicates a lack of electronics knowledge which cannot be filled with a simple reply.

You could use a relay board to turn the motors on/off and control thier direction of rotation. (Look for H-bridge). Speed control can be done by using a frequency controlled square wave to supply power to the motors. There are circuits for doing this. You might have four speeds, stop;slow;medium;fast that would be coded as say 00 01 10 11.

As for inputs you need more than a relay although relays might be used to select which input to read at any particular time.

You have not said what language you would program in?

JC