Technically yes, but we commonly refer to members of the House as congressmen/women and members of the Senate as senators. Being a senator gives you more power because there are only 100 of them compared to 435 House members, so it is a meaningful distinction to make.

https://en.m.wikipedia.org/wiki/First_lady https://en.m.wikipedia.org/wiki/Second_lady

Many do, though the title is perhaps not used as often in most as it is in USA

What? The term “second lady” most certainly existed long before this.