If I could convince her to list it for $2.9M or $2.8M and work with me; how could I get her house sold and find a buyer willing to pay this amount? 

It could be worth checking out other custodians, not just the ones with checkbook ability, because you may find that they offer the quick turn around and funding times you are looking to achieve with that checkbook ability.

Assuming I find another multifamily that would cash flow, how would you all finance the deal.

Tom, were you ever able to find a company or individual that purchases remainderman interest? 

If you find one that goes below 680 the rate will be horrible 8's 9's and at that point its not worth it and ruins cash flow.

You might find that "saving" on taxes is small compared to what the property might be worth (talk with a trusted real estate agent who knows the area and can give a projection of property values).Don't forget to factor in closing costs (real estate fees, pro-rated property taxes, etc) and take into consideration your other income and/or investments. 

It seems like you can find Lakefront properties for under 500K and wanted to talk to any investors who own property there to get a sense of the market and what kind of numbers they are seeing.

You can also find MTR rental amounts on furnished finder.

What I am finding is that the lots within HOAs sell for double or even triple of lots in regular communities.

However, our concern is that it would be difficult to find a tenant in those areas.