I got a rental application by a couple with 3 kids for one of my property. 

Which is this application/website?

My loan application was denied because my salary from my full-time job is too low.

The Impact on Mortgage RefinancingLast week's decline in mortgage rates has already led to a surge in refinancing applications, with activity rising by 20% week-over-week, according to Fannie Mae.

The combination should help you develop new strategies (money applications), and how and where to apply these strategies.2 - You don't need money, at least your own money. 

Cost could change but the bigger issue is making sure the usage is still eligible for the type of policy you have.As an example, at the time of application, a company might ask are all lease agreements for one year or longer. 

Not that much in savings, married to a nonAmerican (visa costs= not fun).

And, if the money is borrowed and you lie on your loan application about that (they will explicitly ask and you will have to explicitly lie if you want the loan) then you're committing loan fraud.If you have to turn right around and sell this property for some reason, I,as the lender of the 20% down, will suffer a 50% loss. 

Do you think the tips in the guide, Real Estate Investing For Beginners, are still applicable in 2024 and beyond?

I would start the whole process over with the tenant - application, screening, and approval.