Here "cup" refers to what Jesus must suffer. Suffering is often referred to as drinking from a cup. AT: "drink the cup of suffering that I will drink" or "drink from the cup of suffering that I will drink from" (See: [[rc://en/ta/man/translate/figs-metaphor]])
Here "baptism" also refers to what Jesus must suffer. Just as water covers a person during baptism, suffering will overwhelm Jesus. AT: "endure the baptism of suffering" (See: [[rc://en/ta/man/translate/figs-metaphor]])
# We are able
They respond this way, meaning that they are able to drink the same cup and endure the same baptism. (See: [[rc://en/ta/man/translate/figs-ellipsis]])
# you will drink
"you will drink as well"
# with which I am baptized
This can be stated in active form. AT: "which I will endure" (See: [[rc://en/ta/man/translate/figs-activepassive]])
# But who is to sit at my right hand ... is not mine to give
"But I am not the one who allows people to sit at my right hand or my left hand"
# but it is for those for whom it has been prepared
"but those places are for those for whom they have been prepared." The word "it" refers to the places to his right hand and to his left hand.