No, the alt-right is an alternative to the previous right ("alt" is short for "alternative"). They're more racially focused and less libertarian.
I'm not following this.
What's happened mostly in America is that Southern conservatives have left the Democratic Party and moved to the GOP, while Northern liberals have done the opposite, which has had the effect of making the average Democrat more left-leaning and the average Republican more right-leaning. But additionally, as Republicans have developed their own alternative media system, they're cut off from objective reality and so have moved further right because of that. There have been some other changes that have moved things a little one way or the other that aren't really ideological (like, recent research on the impact of MW increases have led more liberals to support further increases, though on the flip side, the political difficulty involved in any change has made the current level lower if we adjust for inflation or overall growth). Another interesting dynamic is healthcare. Democrats have long wanted single payer, but had continuously failed to get past the political hurdles, so they moved right in terms of aim and were actually able to enact reform that moved our system left. In terms of social issues, I guess you mean like more widespread acceptance of same-sex marriage and of gays just generally being able to live their lives, sure. But that's a broader cultural change more than a political issue.