Oof, I did a lot of “Check Letters” on this one. The puzzle beat me.
15A, Estate taxes, e.g. – INTERNALREVENUE
17A, Grosbeak relatives – SCARLETTANAGERS
50A, Tons of work to do – ALOTONONESPLATE
53A, Carnival offerings – PLEASURECRUISES
2D, Without reservations – UNCONDITIONALLY
3D, Try to get a better view, say – STANDONONESTOES
12D, Operator’s line – ONEMOMENTPLEASE
13D, It included the Eastern and Western fronts – EUROPEANTHEATER