When a user logs in using live forms, I would like to redirect them to the users activity page where they can see their activity and update their profile.

 Live Forms uses DNN settings for redirecting after login so It is not possible at this time to override DNN setting. Please add this to our Community Ideas

I set the site settings to redirect to the activity page but it does not include the userid. Is there a way to redirect and specify the userid in the url.  It should like like this mysite.com/activity-feed/userid/1

Unfortunatly, It is not possible at this time. Please add this to our Community Ideas 

Why is it that the redirect function in live forms is disabled in the log in form? It would be helpful to be able to override the site settings for an instance of the module. So for instance in site settings, redirect would be turned off so the return url would be default but in another instance of the module I could specify a redirect using tokens in the url.

It is by design that if you use login action in Live Forms then you cannot create redirect action. Live Forms use DNN's settings to redirect after login so it is not possible to override at this time.  Please add this to our Community Ideas