grammar - Is へ and に interchangeable in these cases?

I'm just starting to learn Japanese. I am not quite understand about one of the uses of the captioned particles. I've learned that に refers to the location of destination, and へ refers to the direction of the destination. But my friend told me they are interchangeable and に is colloquial and へ is for writing. If yes, in below cases are they interchangeable?

1. 川の 向こうへ 渡る 橋は 一つしかありませんでした。


2. 友達と レストランへ 行きます。


3. 来月 国へ 帰ります。

Will the meanings be different if へ is changed to に? If yes, what difference will be?

Thanks!!