2 Marathons in 2 Weekends

After being unable to run London last weekend because of a late injury (Sprained Ankle) in training, I am now looking at doing an Autumn Marathon instead. I am thinking Amsterdam, but also like the idea of doing Frankfurt the weekend afterwards.

At Amsterdam I would be looking at going under 3 hours (for comparison, I did 3:20 last year but have come on a lot more, was aiming for 3:10 at London, and that is running only 2/3 times per week through triathlon training, and recently set my first sub-36;00 10k pb.) but I would be happy with anything sub 3:30 at Frankfurt

Has anybody done this? I know I could do them both and just get round, but I will give everything on the first one to try and break  hours (and definitely get a GFA time of 3:10 if I dont) and don't know how much it will take out of me. I won't start training properly until mid July as I have an Ironman on 1st July and will need 2/3 weeks to fully recover