Honoring parents includes our common parent Hashem. The Sabbath takes precedence as even our parents are bound to respect their parent, Hashem. The second tablet covers potentially capital crimes between man and man. Murder is one prohibition. Not to steal refers to kidnapping.
Monetary theft is covered elsewhere.
The proper warning for each prohibition is also spelled out later. The Creator spoke to the myriad of Jews assembled the first two commands. Hashem wrote the first two tablets whose pieces are kept in the ark with the second set inscribed by Moshe. The 'Erev Rav' of nations around the world were also witnesses. Displaying the tablets testifies to the revelation at Sinai.