Sites with big collection of ebooks in chinese language, but western titles mostly
If you are not restricted to "free ebooks only", some online ebook stores are available, like amazon.cn, book.jd.com, and book.douban.com.

As for free ebooks, it is highly unlikely to get free legal copies of the ebooks you mentioned, especially the western titles with Chinese translation. After all, China does not have a long history of EN to CN literate translation, and many of these venerated translators are still alive.