The letter 6475 is for the third stimulus payment (not the advance child tax credit) ... so how much did you get total did you get between you? Did you have 4 people on the 2020 return ? If so and you filed a joint return then you would enter the $5600 (1400 x 4) when asked. If there was only 2 people on the 2020 return then you only got 2800 (1400 x 2) then enter only the 2800.
If you each also got a letter 6419 for the advance child tax credit then you must enter the amount as printed on both letters as instructed.
