This is the 10807th most frequent Korean word.
그들도
"They too" or "they also."
Here, '그들도' includes 'also,' indicating that 'they' (그들) were invited along with others.
그들도 파티에 초대받았습니다.
They were also invited to the party.
In this case, '그들도' suggests that 'they' made an attempt in addition to others trying to solve the problem.
그들도 문제를 해결하려고 했습니다.
They also tried to solve the problem.
'그들도' here implies that 'they' offered ideas too, alongside others' contributions.