I just released a new course on RV Park investing and also have an eBook on Building an RV Park.  

Any recommendation on a book, e-book or other resource that you have come across which explain this strategy in details?

The free Ebook from BP and Gary Keller's Millionaire Real Estate Investor are two good places to start.But also remember, you cannot learn everything before you start.

@Jay Hinrichs  has just publish a ebook for out of state investors, send him an email for a copy.

My wife has a YouTube/Social Media business (youtube ad revenue, selling of ebooks/courses, brand sponsorships, etc) and it would be a bonus (but not required) for this person to be knowledgeable about tax strategies for this type of business as well.

I also include an ebook they can download to provide the seller with more value.

I can't tell you if the partnership with your cousin is right or not without knowing either of you but the characteristics of a good partnership are complimentary skillsets, an operating agreement that clearly states who does what when and who gets what when, equal risk and equal motivation, constant and honest communication, and following a clear business plan. 

Gain valuable and complimentary experience.

The information is very limited.Is there any Ebook / Webinar specifically on Mortgage Surplus Funds?  

A couple of books that I've read was a an ebook by Daniel Wiafe and Robert Shemin boyh were great books on wholesaling!