You could read the Module 2 (or whatever module you’re on) for school time and then read the Module 1 literature to your 6yo before bed or during rest time or something. The 6yo would be essentially getting two modules at once, but it’s not going to hurt him. He would also probably enjoy undivided Mommy attention.
Or, you could read Module 2 to the 8yo at a certain time of day and read Module 1 to the 6yo at a certain time of day, giving both children Mommy time.
My last suggestion would be to read only Module 2 literature to both children and save Module 1 for when the 6yo is old enough to read them on his own (maybe around age 7 or 8).
Hope that helps,
Lindsey