We were there last summer and we found (without excessive hunting, just going to the kiosk) that we could get most things at MK, especially characters (not A&E). We could not get 7DMT as a 4th either. At EPCOT, we could get anything except for Soarin' or Test Track. We even saw Illuminations as an option late in the afternoon once. Everything at AK was available and Everything except Toy Story and RnR was available at HS.
4th FP+ availability also depends on your group size. Sometimes we were able to only get a single FP for a character so only one parent could go with DS to the M&G. We could get Illuminations for 4 or 5 but not our whole party of 8. The fewer the people, the more that is available.