Combine businesses or keep them separate for SEO

Hey, r/SEO thank you for taking the time to read this!

I manage 2 yacht charter companies in San Diego, CA, and have 2 more yachts on the way! We will have a total of 4 yachts that we will be chartering.

That being said, the 2 yacht charters are currently different companies with different websites. Now that we have 2 more on the way, I am wondering if I should make them their own websites and market them all separately or combine all 4 yachts into one big company and do SEO and marketing from one website. On the other hand, if I do SEO for all 4 yacht charter companies it is quite possible that I could own the majority of the first-page Google results. Does anyone have some advice?