I'm married, have three kids, and I live in an upper-middle class type suburb with the lawn and the white picket fence and it costs so much these days to keep a family there, it makes me worry about the future for my kids. 

I’m married, and my wife and I have a 5-year-old son who keeps us on our toes!

We were married over a year ago and I moved into her condo and we put the other condo up as a short term rental. 

Filing separately in most cases hurts married couples, tax-wise.

As the saying goes "Date the rate, marry the home" 

Holding EXEMPT (from bankruptcy forfeiture) assets, holding assets in exempt entities (retirement accounts, pensions, IRAs, in some states insurance and annuities), homestead exemption, remote entity protection (LLC, Serial LLC, Corporations, Limited Partnerships,) Asset Protection Trusts, using separation of assets for married individuals (in certain states) charitable remainder trust, etc. can be very effective though can be costly. 

Convert the Property to a Primary Residence: If you live in the property for at least two of the five years before selling, you may qualify for the primary residence exclusion, which allows you to exclude up to $250,000 of capital gains ($500,000 for married couples) from taxation.4.

Lived in the upstairs unit for 3 years until I got married and bought a house What made you interested in investing in this type of deal?

  :)   Or marry a full-time Realtor.Are you going to run a syndication or just give them money to invest?

If they are married/related yes, combining incomes to reach the goal is generally acceptable.