Karl Marx and Frederick Engels
interesting, do they use the exact words?
It may be that folks such as your family members don't realize the Marxist foundation of the modern Democrat Party. In fact, I doubt that many rank-and-file Democrats do understand the Marxist basis of their party. They are seduced by false claims that the Democrats represent the little guy, or that Republicans are meanies who want to get into everyone's bedroom, or the siren song that government is the solution to all sorts of problems, etc.
A great many Americans also don't understand the legacy of our founding period and the type of government the founders bequeathed to us. Many present-day Americans are immigrants or the children and grandchildren of mostly European immigrants who came here at the end of the 19th and beginning of the 20th centuries, when Marxist ideas were new, popular throughout Europe, and seemed to hold the promise of a better future for the masses. They brought those ideas to America with them and changed this country accordingly.
I don't have time now to go into it in detail, but StriperSniper is right. If you read even a synopsis of the Communist Manifesto, you'll learn what the Democrat Party (and all modern Leftist movements) are all about.