yeah i wouldn't worry too much about the flights within europe. i would much more worry about the flights across the atlanic, as its high season,even if there are several options with lh/af it might get tough.but if you are flexible you should get on one of those flights. maybe you have an agreement also with az, which also departs from terminal 1 in jfk also there is os and in general with an ticket issued on lh you shouldn't have a problem getting on an os flight, wich also departs terminal 1, so you don't have to change terminals in jfk which it might make a little bit easier...