Questions on the Congress reading

Assuming there were a way to measure how divided ideologically a Congress is, does that division go down or up when congressmen read the bills?

Prof. Pitney and Prof. Bessette argue that there is a weak link between interest groups and floor votes. Which scholars have said that first?

I've read elsewhere that interest groups tend to draft all of some bills. How is that legal? How does that relate to the Congress chapter?