Engine turns over not firing after oil pressure low engine stop engine warning.

(background purchased in 2013, had check engine light on dealer said it was o2 sensor and gave us a promissory work order to have it fixed. Dealer only cleared codes and light came back on. Car was always slow, labored to start like a low battery, however battery showed proper voltage. Dealer refused to make good on promise said it was a battery problem and we needed to replace the battery. fast forward to 2016 still using the same battery ac stopped working), six months later Low oil stop engine light came on. Husband stopped checked oil and it was in proper operating range so he added more. Engine was hard to start but eventually did. Drove home 1 mile and parked it tried to start it and again hard start, ran for less than a minute and turned it off. Checked oil again tried to start engine and only got a quiet spinning noise. Changed starter, now engine sounds like it is turning over but now sounds like only 1 or 2 cylinders make an attempt to fire two firing noises back to back then no more firing just the engine spinning. obd reader shows no codes. Other interesting things to note. can hear what i believe to be the fuel pump running when key is turned half way. When changing the starter we removed the oil filter without draining the oil. Very little oil came out.