I am newly married and have a hefty mortgage myself, but I manage to save a decent amount of money realistically 10-15k a year I have been working as a construction worker as long as I have been working I am a mason by trade and even though moneys tight I know I will be a successful investor even in the current market.

So if I understand this correctly, by qualifying to extend the 5 year rule to 10 yrs, $250k if single or $500k if married of proceeds from this sale would be exempt from capital gains? 

For your primary residence, you can exclude up to $250K (single) or $500K (married filing jointly) of capital gains if you’ve lived there for two of the last five years.

If they get married it will help her earn SS benefits, etc etc. 

Memo 2014-160), where the taxpayer lost business use deductions due to personal use.

My fiancée and I are getting married in November and will be moving into a different rental in another part of town shortly after.

For reference, I am 30 years old and not married.

This defers capital gains and depreciation recapture taxes on the sale of your fourplex.After converting it into your primary residence, you may qualify for the primary residence capital gains exclusion ($250K single/$500K married), but only for appreciation after the conversion; gains from the rental period remain taxable.

It can be done ethically, but you need safeguards to confirm mortgage & possibly property tax payments made on-time, as well as insurance with you protected.- Also, you need a legal way to take back the deed if buyer defaults!

All the IRS cares is that the taxpayer is the same.