1.

What does Sylvia's father think?

He thinks it is the first time there have been such changes in Europe without a major war.

2.

What doesn't convince Diana?

The way so much power is being concentrated in Brussels doesn't convince Diana.

3.

What does Diana refer to as "cultural and economic differences"?

She refers to the many cultural and economic differences between different countries in Europe.

4.

Why doesn't Sylvia approve of the plans for a single currency?

Because she thinks (that) the currency is a part of their culture.