I have 5 properties I have deeded to an LLC (bank ok'd it), but debt in my name, I want to refinance to commercial loans to get the debt out of my name.

Beyond that - if it's an LLC then how can I be more liable? 

If you form an LLC, and allow the operator to manage the LLC, you can avoid the tax burden.

I have formed a LLC for the rental property and registered in California.

I've had my Series 6 financial license (expired), I have my real estate license in TX (active) and I've been around the block with STR, long term rentals, private placement investments for qualified investors and the stock market / mutual funds / ETFs.

I have a 50/50 LLC with my business partner.

We don’t know any PMCs to recommend in the area mentioned, but since selecting the wrong PMC is usually more harmful than selecting a bad tenant, you might want to read our series about “How to Screen a PMC Better than a Tenant”:https://www.biggerpockets.com/member-blogs/3094/91877-how-to-screen-a-pmc-better-than-a-tenant-part-1-services-and-processesWe recommend you get management contracts from several PMCs and compare the services they cover and, more importantly, what they each DO NOT cover.

I have an opportunity to buy 19 SFH under on LLC.

I am fairly new to the MF investing and have a few questions.1) Can a loan be applied under LLC or has to be applied by the partners of the LLC?

If they are all on separate policies but owned by the same person or same LLC, maybe yes.