You mention two different topics.

Professional philosophers do essentially the same thing we do, they derive a set of personal beliefs that they see as trustworthy. The difference is that they go out and try to sell their philosophies to the public as if they were universal, but they aren't, so they almost always fail. Their books and publications tend to be filed under the heading "OPINIONS".

The second topic you mention is about the role of epistemology, in theory the study of knowledge but in practice an amalgam of (once again) opinions from different philosophers. It's difficult to explain epistemology without referring to those opinions, and those may be wrong anyway. Several pieces of the puzzle are still missing.