They are the 5 blog templates/layout we provide by default it's not customizable.

I suggest you two ways to work on your blog a very customizable way :

1 - Create a non published article that you will use as your template and copy paste it (as format is conserved) if you need to work on the same basis.

2 - Only use titles and paragraphs and don't change font-family, font-size, etc here but do it in your pagebuilder blog article details page using CSS so you're 100% sure it's consistent between your different articles.