York Family Sidebar?

Hi guys, 

I've been struggling with my blog page for a while now. Turns out I created the entire website on one of the least flexible template on Squarespace and it is really frustrating...

Anyways, I'm trying to add a sidebar on my blog post page but can't seem to do it, at least, not automatically...

Can anyone please help me out? Is there a way to force it onto the website? 

Many thanks

Thank you for the help. 

I'll start work on it.