Considering the questions:
Why did Judas kiss Jesus? and
Why did Thomas doubt the resurrection?
Key factors in understanding what happened and why:
The Jewish leaders wanted to have Jesus arrested, and sent soldiers to arrest him several times, but they were unsuccessful, with Jesus melting into the crowd or leaving.
John 5:13 “The man who was healed had no idea who it was, for Jesus has slipped away …”
John 7:30 “At this they tried to seize him, but no one laid a hand on him.
John 8:59 “At this, they picked up stones to stone him, but Jesus hid himself…”
John 10:39 “Again they tried to seize him, but he escaped their grasp.”
They had argued with him many times in the past, but now need someone to specifically identify him for them.
Mark 14:10-11 “Then Judas Iscariot, one of the twelve, went to the chief priests to betray Jesus to them. They were delighted to hear this and promised to give him money.”
Matthew 26:48, 49 “Now the betrayer had arranged a signal with them: ‘The one I kiss is the man; arrest him.’ Going at once to Jesus, Judas said ‘Greetings, Rabbi!’ and kissed him.”
Judas was a thief, and figured out a way to make extra cash by leading them to Jesus. If he expected Jesus to melt through the crowd as before, he could turn this into recurring income.
John 12:6 “He did not say this because he cared about the poor but because he was a thief; as keeper of the money bag, he used to help himself to what was put into it.”
Six days before the betrayal Jesus was anointed with $50,000.00 worth of perfume “for my burial.” Judas could have just said “Follow your nose. He still smells of the perfume Mary poured on him a few days ago.” John 12:3. Instead, Judas has to be onsite and specific in his identification. Mark 14:44
Thomas is nicknamed “the Twin” but only John tells us this. John 11:16, 20:24, 21:2. When the decision is made to go to Bethany (to raise Lazarus) Thomas says “Let us also go, that we may die with him.” He expects that if the Jews kill Jesus they will also kill him, and the rest of the disciples. John 11:16.
So we see that Thomas’s doubt is related to his fierce loyalty to Jesus. If the rulers of the Jews really want to make sure they get Jesus they will need to get Thomas, his “twin” or doppelganger. Judas has no desire to give the Jews the easy (and free) out of following their noses. His kiss was not expected to get Jesus killed, just to get Judas paid (again and again), and the resulting death of Jesus leads to Judas killing himself.
For Thomas, if he could be a replica of Jesus, so could someone else. Thus he has to see Jesus alive with his own eyes to believe it.