i very rarely trust fish from any big box store to be healthy. always good to quarantine all new fish for at least a month before adding them to your main tank, to avoid disease and parasites from infecting everything in your main tank.
mollies are pigs! lol. so IMO they add a good bit to the bioload of a tank. but that trace of ammonia was most likely from the dead angel decomposing. what was the time frame between adding the mollies and finding the angel dead?
as for filter current, i've had two angels do just fine when i first got them, in a 20 gallon with a rena xp2 canister on it. i was using the spray bar, so that did cut down on filter flow a bit, but the tank only had a couple small calm areas which i rarely saw the angels swimming in. both these angels were quite small, but were a bit bigger than nickel size when i got them.
your ph is just fine. if the fish were bought locally at a big box store then they were most likely in water very much the same as your tank (if you don't do anything to buffer or adjust the water in your tanks), as big box stores don't take a whole lot of time or effort to make changes to the water to soften or harden it any. my ph is 7.8/7.9 constantly out of the tap, and for some reason doesn't change at all in my tanks. my two angels were thriving, grew huge, and were full of attitude, lol.
perhaps set up a separate quarantine tank at home, a 10 or 20 gallon would work, and grow out an angel in there until they are a bit bigger and hardier, then move them to the school tank? IMO a 29 gallon tank is just big enough for one angel to be a centrepiece if the rest of the stocking is light.