it's kind of kind to understand the concept of trinity, and different people might give different illustrations. 2 of the illustrations that i use the most would be:
illus 1:
think of a cup of milk coffee. a milk coffee is only a milk coffee when there is black coffee, sugar/creamer and milk, they are 3 but yet known as 1, milk coffee. it's not a complete picture, but it can be absorbed easily by many people who first come across this trinity issue.
illus 2:
think of your father. your father is a father, at the same time, he is a man, and he is also a husband. this illustration is also pretty simple and straight forward.
if i remembered correctly, there is one question posed mentioning that "your God is weaker than a bunch of jews". to reply this, there are many point, but the host didn't even mention 1 of them.

(by the way, after some googling, seems like the video is made by anti-christians and the channel does not really exists) alright, some answers

Jesus died in the form of a man. Jesus was a man in nature, but a God in identity. there for the man can die, but the identity of God remains. this is not going to be easily explained... i give up explaining this through online forum.

. apart from that, Jesus' crucifixion is part of God's plan. an animal need to be sacrificed so that the sin of man can be put on to the animal and the animal die in place of the human. it's also similar to Muslims, Hari Raya Korban. to carry the sins for all, a pure spotless being is needed. therefore Jesus came.