I want to purchase an investment condo for $150,000.I want to get Heloc loan from my other investment condo for $50,000 and use it as downtown payment for this condo.Can I get a 30 year fixed conventional loan for $100,000 and use $50,000 for down payment from heloc?

Quote from @Brandon Croucier: The loans are available but nobody wants to do them.There always seems to be something wrong with the properties, as lenders we just can't make enough $ for our time.9/10 Borrowers also complain about the "excessive fees" for the loan amount.If you are okay with paying 8k in closing costs then the loan is available. 

Once construction is complete you could refinance out of the construction loan into a DSCR loan.

It varies for me city by city here in south Florida.

Option 1: The loan that the owner has is an assumable loan at a 3.875% rate and still has about $265K.

A lot of the owner occupy loans require you to live there for at least a year, so it's not forever. 

I would get an attorney or title company involved to create your loan documents to ensure they comply with the law and cover all the aspects you need.Another method that is likely your best bet to take on investors is to create a joint venture (JV).

FHA loan through my mortgage broker associates.

You would need to let them know you are 2nd lender and want to pay the loan off.

I've been pre-approved for a bank loan but haven't thought about someone with experience working with investors for deals.