I've given google's programmable search a list of sites, for now I'm starting with:

But when I search any query, I get pretty much only YouTube results, which I believe is because YouTube has the highest page rankings.

Is there any way to customize this to be more balanced among the different sites?

See below for more detail for what I'm thinking.

Possible Solution #1: Round-Robin

The top result from the first site displayed, then the next site, and so on, until all sites have had their top search result displayed, then starting over.

Possible Solution #2: Site-to-Page Rank Ratio

Let's pretend that youtube's site "rating" is a 10, and reddit's is a 5. Now, in a list of search results, let's say that youtube.com/some-result has a rating of 8, and reddit.com/some-other-result has a rating of 6. In this case, the reddit.com result should display first, even though the youtube.com result has a higher absolute ranking. The reddit page's page-to-site ratio is higher.

I have no idea if #2 would even be possible, but maybe it can serve as an illustration for what I'm looking for. I'd be plenty happy with a simple #1 Round Robin approach.