This is the 17013th most frequent Polish word.
wysłali
"Sent" (past tense of "send").
The word 'wysłali' here refers to the act of sending (past tense, third person plural) something by mail.
Wczoraj wysłali paczkę pocztą.
Yesterday, they sent a package by mail.
In this sentence, 'wysłali' is used to ask if the act of sending (past tense, third person plural) documents has already occurred.
Czy oni wysłali już te dokumenty?
Have they sent those documents yet?
Here, 'wysłali' refers to the uncertainty about whether the action of sending (past tense, third person plural) invitations was completed in a timely manner.