Sorry for the troubles. I wasn’t able to work in last few week due to some unavoidable issues. We are currently working on fixing the issues with the theme but many times it is the combination of theme+plugin which creates the problem.
For eg. on dchistory.org site, the slider issue is due to a css class defined in in espress_default.css which is getting included by the event espresso plugin. A temporary solution to fix that issue would be adding the following custom css but need to test it further to make sure it doesn’t break anything else.