@Chris Mitch If I'm understanding correctly, you sold a property for $950K with $600K in cash proceeds after closing costs and debt payoff. If this is the case - and you want a complete tax deferral - you would want to not only purchase one or more replacement properties that are equal or great in value than the relinquished property, but you would want to use all of your cash proceeds. Any leftover cash proceeds at the end of the exchange is considered cash boot and is taxed.
In your case, you have purchased replacement property at a higher value, but you've only used up $400K of your $600K in exchange proceeds held at the QI. If you want a complete tax deferral, I'd suggest using more cash for property #2 that hasn't closed yet - especially since you only plan to put $105K toward property #3.
As far as property #3 goes, this would be allowable as long as you make sure you are on the title/deed as a tenants-in-common owner. If the property were to be purchased by the larger entity and you paid for ownership of that entity, it would not qualify for the 1031 exchange since you aren't directly purchasing real estate ownership in that case.