Front-page https://github.com/digitalcraftsman/hugo-agency-theme
Blog https://github.com/eueung/hugo-casper-two git submodule add -f https://github.com/eueung/hugo-casper-two themes/hugo-casper-two
https://gohugo.io/content-management/multilingual/
https://discourse.gohugo.io/t/how-to-combine-two-hugo-themes/3244/3 I would probably just accept that there are two sites (see the multilanguage tutorial) and build one below the other:
So
Site 1 => public/
Blog => public/blog