made our hearts melt = made us dismayed?

I'm sure they were dismayed, however, in this context I believe the author intends to point out a loss of faith.

It is clear.
The Chinese official version of the Bible is ambiguous for this. I hope more native speakers come to verify it.

In modern American usage, to make someone's heart melt means to fill them with emotion, and the implication is usually a positive one: The sight of the happy children made his heart melt with joy.

However, for the passage from Deuteronomy, Chapter One, the meaing can best be derived by reading it in the King James version:

Notwithstanding ye would not go up, but rebelled against the commandment of the LORD your God:

And ye murmured in your tents, and said, Because the LORD hated us, he hath brought us forth out of the land of Egypt, to deliver us into the hand of the Amorites, to destroy us.

Whither shall we go up? our brethren have discouraged our heart, saying, The people is greater and taller than we; the cities are great and walled up to heaven; and moreover we have seen the sons of the Anakims there.

Here, the meaning is clearly one of being dismayed, of giving up hope. This is not how the expression is usually used in contemporary English.

If, in future, you wish to know the meaning of a passage from the bible, i suggest that you give us the citation of Book, Chapter and verse(s). In this case, the Book is Deuteronomy, the Chapter is chapter one, and the passage is verses 26-28.

Lo, the people of A2K rose up, and spake verily. Blessed are they in the eyes of the Lord.

Blessed be him who has many tax-free investments . . .