Welcome aboard. I work for delta. Generally speaking, the fall months are pretty open for the european flights. The only thing to consider is that european schools have fall break in october, but is not nearly as bad as summer. to make the most of your options to get a seat and get business class (if all kids with you are over 8 years old) I would recommend planning for Tues/Wed flights as they are generally the least travelled days.

Like the other posts, its really way to far out to talk about loads...thats the game with buddy passes. Check back in closer to a month out. The employee should be able to direct you about loads firstly, if they can't post and I will check once its worth looking at realistically.

Happy travels man!