Usually the rigging manual will specify the amount of toe or toe out but even that can be misleading. In addition some setups specify zero toe in or out.
It is easy to make twins parallel but a spec like 1/4 inch can be misleading. The trailing measurement is easy, i's the spacing between the two prop shafts (center to center) but the leading edge measurement might be the forward edge of the lower unit or more likely the spacing of the end bolts on the motor tie bar. What is more helpful is a spec that tells you how far off of the transom, the motor wakes meet. 20 to 25 feet is a decent starting point but the reality is that if you want to optimize performance and/or handling, you will have to experiment with different settings at specific speeds. Start with the motors parallel and then add a little extra spacing to the tie bar by adjusting the threaded shaft one or two turns.
To make an initial estimate of your motor alignment, measure the center to center distance of two engine mounting bolts ( the same bolt on each motor). More often then not, that will be 26 inches. Now measure the center to center distance of the motor tie rod spacing. For Yamahas, that might ne a tad more than 26 inches. That tells you that the motors are angled toward each other.
There are those who will tell you to run at speed with the steering disconnected and see where the motors end up and use that as your setting. I think that idea is crazy and wouldn't try it.
To add more confusion to the discussion, different manufacturers use the terms toe in and toe out differently. You may think that the motors should be toed in to make the wakes cross. Granted, the motors will be angled toward each other but technically that is toed out!
You should think of a person standing behind the boat, feet on the ground. The persons feet are the motors, your toes face forward and your heels aft. If you want the motors to angle in towards each other, you would spread the front of your feet wider apart than the heels. Yours feet are toed out
So what most boaters as well as many manufactures call toe in is really toe out!