Isaiah speaks to the people of Judah in the form of a poem. (See: rc://en/ta/man/translate/figs-parallelism)
Possible meanings are 1) Isaiah is saying two different things about them. AT: "Nation of Israel, you sinners" or 2) he is saying only one thing about them. AT: "Nation of sinners"
a people weighed down with iniquity
Something very heavy that a person might carry is a metaphor for their many sins. AT: "their sin is like a heavy bag on their shoulders that makes it hard for them to walk" (See: rc://en/ta/man/translate/figs-metaphor)
offspring of evildoers
The word "offspring" is a metaphor for people who do what others have done. AT: "people who do the same evil they see others doing" (See: rc://en/ta/man/translate/figs-metaphor)
do evil deeds
They have abandoned Yahweh
"They have gone away from Yahweh"
"have refused to obey" or "have refused to respect"
Judah is part of what had been the nation of Israel.
they have estranged themselves from him
Though at one time they were friends, they now treat him as though they do not know him.