Using Two Themes Simultaneously?

I have a feeling this is a very simple answer, so thanks in advance for your patience.

I am using a slightly modified version of this theme:
my site: https://skjfamily.com
theme site: https://www.dimension2k.de/index.php?wptheme=Dimension+2K+-+desert-theme

I want to add this photo blog within the blog above.
https://www.taly.com.ar/tan/

However, I do not want every post at https://skjfamily.com to post within the photoblog, I only want to display specific photos, to make it a portfolio for some of my photography.

Somehow I need to have two themes active at once. Do I need to create another domain or something? I’m very new to this, so please pardon my ignorance.