The irony is that Shylock trusts his daughter to follow his orders and also to share his values in reviling Christians and adhering to Jewish values, but she betrays him on both fronts. He hasn't understood her at all, merely assuming she would be an imitation of himself. She is the last person with whom he should have entrusted his keys, for she plans to rob him and run off with the Christian Launcelot. As she says,

Farewell, and if my fortune be not crost,

I have a father, you a daughter, lost.

Shylock is reluctant to sup with Bassanio because he knows the Christians despise him. They are not asking him out of affection, but to "flatter" him or pretend they like him. He says he will go to get a free meal. As he puts it:

I am not bid for love. They flatter me.

But yet I’ll go in hate to feed upon

The prodigal Christian.

Shylock is reluctant to go to this dinner because he's had dream about his money bags that he sees as a premonition of someone stealing from him. He gives his daughter Jessica his keys so she can lock up the house and keep it safe from anyone who tries to steal from him while he's gone. He also tells her to stay inside and keep out of the Christian revelry going on in the streets. The irony is that Jessica is planning to run away and marry her Christian love, and when she leaves she will take a great deal of his fortune with her.