While I have no experience with breeding GT's, I have kept one up to 5" before I had to sell it and I have bred more than a handful south and central american cichlids including A. pulcher aka blue acara, GT's cousin
1. Parents eating eggs is not uncommon, often the parents will eat eggs that are going bad or have gone bad to help stop other eggs going bad
2. Many cichlids eat there own young the first time or three (most notable are blue ram, apistogramma and angels). Of my current convict pair the male ate well over 1/2 the brood once they got to swimmer stage first two tries, last time, his third he didnt, and thats a convict, so your GT might just need the practice
HTH
Andrew