Then I have to go for HML, with high interest rates and 12 month repayment period.

I didn't pursue because the real estate market was good and rates were at an all time low.

It would be rental property to my parents and I would pay a 60% market rental rate and I would also pay the loan.

I am currently evaluating a multi-family investment opportunity in Anaheim, CAIs there a local commercial broker or property manager who could tell me what the market cap rate is for C class multifamily buildings 10 to 20 units in that area?

If you are making larger orders you can make those through their pro-desk or through their pro-site and get discounted pricing and probably average 15% off!

Recently several of my investor clients have leveraged equity in their primary or investment properties as down payments for purchase acquisitions by obtaining a HELOC or fixed rate second mortgage. 

Definitely check in with @Joseph Chiofalo for Jumbo second home and investor loan products, we just had an unbeatable rate and appraisal waiver here on the coast. 

Also not sure when you bought your primary residence, but most likely rates have risen which means your payment would go up. 

or any recommendations on which is the best Bank/lender to get one with the best rates? 

You would never ask an attorney to lower his rate for doing his job and telling you what to expect.