If galaxy MACS0646-JD (the furthest known object in the universe) is 13.3 billion light years away?

Astronomers believe a lot of things that are mutually exclusive. The honest ones will admit that about half of what they know is wrong, but they don't know which half.

For a long time, one group of astronomers could prove that the universe was not more than 13 billion years old, while a second group using the same data could prove that it was not less than 19 billion years old. Neither group could find any mistake in the other's reasoning.

If you look at something from two positions it appears to shift by some angle depending an how far away it is and the length of your baseline. If you look from opposite sides of the Earth's orbit, that is the longest baseline we have, and accurate measurements can be made out to about 3200 light years. Beyond that we are guessing. Highly scientific guessing, but guessing all the same. That is why when you try to look up the biggest stars, the figures get very uncertain beyond 3200 light years.

A big part of science is conjecture, which means making up "What if" scenarios. Often those scenarios get discussed a lot for a long time, and people begin to assume they are true just because they keep hearing them. The big bang is one such scenario. The big bang exists only in somebody's imagination. It was needed to explain implications of the expanding universe conjecture, which was needed to explain the receding galaxy conjecture, which was based on the observed red shift in light from galaxies and the assumption that the red shift is caused by the Doppler effect. If that assumption is wrong then the entire collection of conjectures is without support. There are other possible causes of red shift.

Science is supposed to be based on observations, tests, and proofs. There is a strong tendency to accept conjectures, math models, and consensus of opinions instead. You need to be careful about accepting things that have not actually been observed.