How do I make the measure size equal across all parts, even when I am viewing them individually?

What I am trying to do is somehow format a score not so that all the measures are equal size to each other, they are still dynamic depending on their content, but across different parts the corresponding measures are of equal size, even when I do not view them all at the same time. In further explanation:

For piano 1, the second line of measures (I think it is called a system?) starts with measure 7
For piano 2, the second line starts with 10

This is not what I want. It should be where they both start with 7 on line 2, and with the same number for every line, because they (should) have equal corresponding measure sizes.
(again, I mean when I view them individually, so please don't say that they are already like this because you think I am talking about when I view both parts at the same time)