It depends on your fitness level, your base and your goals. If I were running them just to run them (ie, no definite time goal, not trying for a PR or an AG award), I would feel comfortable running 8-12 miles for my long run on the non-race weekends. On the other hand, I am used to a long (8-10 miles) runs on a weekly basis, so I wouldn't be doing anything out of the ordinary.
If I were trying for a specific time, I would take one race easy, run the other hard, and keep my long runs about 8 miles, or maybe an easy and slow 10. I'd probably keep my speed work to a minimum between the two races as well.