After six months on the market, we received no commucation nor any potential tenant inquiries which we found to be extremely strange given the good shape of the house and pricing.At last we decided to take the property back. 

That was 4 or 5 months ago and no issue from the lender yet (Fingers crossed).

I've included an example below to help illustrate this.So different lenders have different rates (which do vary even for DSCR loans) but these are factors they all consider.See example below:DSCR < 1Principal + Interest = $1,700Taxes = $350, Insurance = $100, Association Dues = $50Total PITIA = $2200Rent = $2000DSCR = Rent/PITIA = 2000/2200 = 0.91Since the DSCR is 0.91, we know the expenses are greater than the income of the property.DSCR >1Principal + Interest = $1,500Taxes = $250, Insurance = $100, Association Dues = $25Total PITIA = $1875 Rent = $2300DSCR = Rent/PITIA = 2300/1875 = 1.23If a purchase, you also generally need reserves / savings to show you have 3-6 month payments of PITIA (principal / interest (mortgage payment), property taxes and insurance and HOA (if applicable).

Purchase price: $1,800,000 Cash invested: $960,000120ft tunnel carwash with 3 detail bays and an upstairs business office. rebranded the carwash business to match the same name and logo as two other carwashes and offered a joint monthly unlimited wash pass that was usable at any of the three wash sites!

I have stayed at an AirBnb for a month in the past but no interested in doing that.

Move to increase rents and do the upgrades earlier, don’t wait 18 months.

The RGV itself has several great investments and worth investing here for multi family.I recently sold a 18 unit a month ago and my same investor is purchasing another 36 unit from me and after funding he'll be picking up another 38 from us, this gives you an idea of opportunity in the area. 

I am completely new to BiggerPockets. 20yo, got my real estate license in TX about a month ago and I began interviewing with different brokers but haven’t really quite found my fit.

Given our current properties, is there a creative way to do the financing that would allow us to buy the beach house without losing our current rental income ($6250/month) we are relying on? 

You will likely pay less than half the addition cost, be able to obtain convention f/f financing, will not have to do the work, will not have to deal with a construction zone, will not have cash outlay months before first associated income, etc.