"їм подобається каша риба і яйця" Should be accepted! Natural Ukrainians use подобається when they say "I like". "To them is pleasing" should be accepted.
You're absolutely right, I have no idea why it was overlooked. Fixed it.
why do яйця not have an accusative form? is it a special exception or something? I've noticed this specific word do this in several questions
The nominative and accusative of this (plural) word are the same. This is typical of neuter nouns: nominative and accusative plural both end -a or -я.