The built in Blog page type isn’t really any good for positioning text and images in the way you want I’m afraid. As you’re discovering, it doesn’t have the kind of control over layout that you’re looking for and I fear you’ll just become frustrated with your lack of progress.
Unless there’s a reason you need to use the built in blog, there are much better alternatives which will give you more control over the appearance. For this you’ll need the Stacks plugin from YourHead. That comes with a selection of layout types for images, columns, text etc. that may be enough for your needs. Otherwise, something like the Poster stack can be used to create a blog that’s much more modern and gives you more design freedom.