I wondered what they might have sung. I read that Passover tradition was to sing from the Psalms, closing with Psalm 118.
I thought of Jesus singing these words, knowing that suffering and death on the cross were only hours ahead
The stone the builders rejected
has become the cornerstone;
the Lord has done this,
and it is marvelous in our eyes,
The Lord has done it this very day;
let us rejoice today and be glad.
Psalm 118:22-24 NIV