I suggest saving the documents as unformated HTML then letting Sigil apply the formatting. MS Word always turned simple HTML into a raging mess that was nearly impossible to read if you let it hardcode the formatting, but it did okay if you let it create generic, non-formatted HTML. I'm talking about the convoluted CSS garbage Word creates. I assume the same is true for most any document editor like Word, Pages, etc. And the same is likely true of creating ePubs directly with those editors. The CSS will be total garbage and difficult to edit. Start with a blank slate and use Sigil to add a bit of formatting where needed.