Owner-occupying a small multi-family property is a smart move—you're reducing your own housing costs while building equity and generating rental income.

Are there other ways to reduce my mortgage that I am not aware of (besides refinancing)?

The cost should be getting reduced significantly. 

He's very thorough with this standard inspections and he also offers "investor due diligence" inspections at a reduced rate.

I'm a small landlord with one tenant (I have two tenants total) in San Bernardino County who stopped paying rent since June 2020, making different claims--work hours reduced and that he's "having difficult times because his coworker died from COVID".

This approach not only keeps tenants happy but also helps you maintain long-term cash flow by reducing turnover costs.

Increase earnings, reduce expenses, save, and invest.

Partnering with others can reduce risk and access better deals.

The reason to do so is not necessarily to reduce cost but to be efficient.

The investors accepted it.  3 months later the buyer tried to reduce the purchase price to $2.6M to stiff arm the investors.