We are also highly interested in building short term rentals such as eco airbnb's, as the cash flow of that route and the small footprint/simplicity of that direction would work well with our family. 

Before going this route, I did a lot of research on other Airbnb's in La Mesa and discovered there are 4 other listings that have hundreds of reviews, which means they have been renting out their trailers on the website for years.Everything was going smooth until a compliance officer from the city knocked on our door and told us we are not allowed to have anyone in it and we need to bring in the awning/ slider and disconnect from the utilities.

So that might be a better route for your numbers before working up to a quad. 

The cheaper route would be to negotiate with kids.

If there’s equity, and all lien holders can get a full payoff - you have more leverage to ask the bank to postpone the auction to get the bank paid in full.If underwater, going down the route of attempting a short sale can take much longer and the lenders may not be as willing if there is an auction right around the corner.. for example, property must be listed in MLS, homeowners must complete full financial package for lender, bank must complete an appraisal, your offer needs to be reviewed by the bank, etc.Completing a sale right before an auction can definitely be done - and we do it all the time - but I guess it just depends on the specific situation.

Look at the intersection. 

I'll make sure to stay on my toes if I do go that route.

I believe you have many options but you first need to know where you are, where you want to be, and map out a route of  how to get to your final destination.

FHA has certain requirments when buying a home and the condition that it is in, so just be aware of that when thinking of looking at fixers. 2. 203k loans can be something you explore if fixers are the route you want to go.3. construction loans (to my knowledge) are not accessible to people who do not own the land outright. meaning you cant have a loan on the house and then get a construction loan...

In that case, I think a hard money or private lender would be a good route.