I provide links in the article. When you see a section that is underlined if you put your cursor over that section you will see the link. So you can just follow the links to find the sources.

Here they are (copied from the article):

https://founders.archives.gov/documents/Jefferson/01-01-02-0161-0004

https://www.constitutionfacts.com/us-declaration-of-independence/drafting-the-declaration/

If this was a research publication, I would repeat the links to sources much more often but in a Medium article I'll just use one link for the main point since I don't need to be as rigorous. However, if you read any of my articles, you will see that I always provide citations and I encourage people to think for themselves and read and interpret the source material I provide vs. just taking things at face value.