Expert Investor Advice Needed - California Inherited Properties

[Derrick StClair]

Calling all experienced investors!!

I'm hoping to leverage this platform of skilled and highly experienced real estate investors to get some insight (or at least ideas) of what I should do to increase my real estate cash flow returns. My family recently inherited 5 properties in San Mateo, California; consisting of (3) single family, (1) duplex, & (1) commercial building. What I'm looking to do is analyze this portfolio and decide what the best course of action is to substantially increase my real estate business keeping in mind that positive cash flow is important. I am new to real estate but have been educating myself substantially over the past 5 months, just hoping to leverage some experienced investors to gauge what they/you would do. 

I'll provide some numbers below to provide more a full picture.

Portfolio: 
note: all properties have zero debt liability (fully paid off) were built in 1922-1965 and have not been renovated since. They could all use quite a bit of rehab work and are currently being rented for 25%-35% below market rental rates due to the condition they are in. 

1) Single Family - 2bd/1ba
Gross Cash Flow = $3,000/mo
Current Market Value: $1.1M

2) Single Family - 2bd/1ba
Gross Cash Flow = $2,700/mo
Current Market Value: $1.1M

3) Single Family - 4bd/2 full bath + 2 half bath
Gross Cash Flow = $0 (Vacant, house need a LOT of work)
Current Market Value: $1.8

4) Duplex - (2) 2bd/1ba
Gross Cash Flow = $4,500/mo
Current Market Value: $1.8M

5) Commercial - 6units
Gross Cash Flow = $11,100/mo
Current Market Value: $2.5M

Total Gross Cash Flow Across 5 Properties: $21,300/month
Approximate Net Cash Flow (after PITI) = ~$14,000/month (property tax assessment is EXTREMELY low because it was inherited, total tax assessment for all 5 properties is <$2k/month)

Market:
Location: San Mateo, California
Neighborhood: Grade B+

In a perfect world I would like to double or even triple this net cash flow so that myself along with my sisters family can retire early. Any help, advice, and guidance is GREATLY APPRECIATED! If there is any information I left out that would be helpful please let me know, happy to share. 

Regards,
Derrick