One way of coping with tiles that vary in size is to mark your area in to bays.
Lay them out dry in a clear area and adjust them by eye till they appear to have an even joint.
Then measure a certain number, whether it be 3,6 or 10, then transfer that measurement to your substrate and repeat that distance over the whole area.
As long as you contain the tiles within that area it’ll all appear to be the same.
With a little adjustment here and there.
Remembering to add a joint at one end of your measurement.
