How do you say in Spanish: they know the answers

Answer 1

"They" definitely means" Ellos" or "Ellas." And definitely is 3rd person plural

As a native Spanish speaker I would say it means : "Ellos (or ellas ) saben las respuestas" is correct

You can also say 'answers' = "soluciones" because questions have solutions too

Answer 2

Probably ellos saben las soluciones, but context matters!

"They" is the plural, 3rd person subject → ellos or ellas.

"Know" comes from to know. In this case, they know answers, which indicates that they know a fact (saber) instead of being familiar with something/someone (conocer). I'd write saben here.

"The answers" can mean a few things. Are these answers to questions (las respuestas)? Solutions to a problem (las soluciones)? I'd recommend rereading the text around this sentence to determine the intended meaning more precisely.