You cannot defer gains anymore on personal use homes (that ended in 1998). You might be able to do a like-kind exchange (sect 1033) if you used the home as rental property, but that is very complicated and you would need to seek professional advice from a CPA, Enrolled Agent, or tax attorney.
Instead of the deferral in pre-98 law, current law allows an exclusion (section 121) of $250k ($500k married) of gain (not proceeds) if the home was your primary residence for a certain period of time. This only applies to your primary residence, not a vacation home. https://www.irs.gov/taxtopics/tc701
If these were not primary residences, you report the 7/17 sale as you would for any capital asset. You do not report the 3/17 purchase, though you should keep all of your record regarding your costs for future sale. See this TT FAQ for how to enter into TT: https://ttlc.intuit.com/questions/2583688-where-do-i-enter-the-sale-of-a-second-home-an-inherited-ho...
You can deduct real estate taxes and mortgage interest for the vacation homes subject to some limitations.
Some useful information here: https://www.investopedia.com/articles/personal-finance/013014/tax-breaks-secondhome-owners.asp
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