Cooking 4 lasagnas at same time
If you can fit all four into one oven and you use convection, just use the instructions for one. Like for all foods, you will want to monitor the progress and possibly decide to give it a few extra minutes or to pull it out a moment sooner. But that is a general advice that takes different oven calibrations etc. into account.

If you use a top &amp; bottom heating element without convection, you might have to do some juggling as you will probably have two lasagnas on an upper and two on a lower rack. This means they will heat / bake unevenly and you should swap upper and lower at about half the given baking time. You might also have to extend the time by a bit, I'd guestimate perhaps ten minutes or so. But the rule of thumb is bubbly = done, so just have a look. Likewise for the final browning step, plan to swap once, watch to make sure nothing burns.