Where are your fixed rate notes at and their respective monthly PITIA payments ?

In this case, your monthly payment with 20% down will have a good MARKET rate if your DTI works with a much lower month payment and no mortgage insurance(MI).

Take the payment in 2 or 3payments.

Would it be wise to buy the land with cash we have or utilize as down payment to avoid PMI?

Prepare financially by saving for down payments, improving your credit score, and setting aside emergency reserves.

Monthly payments are fixed.  

Or a seller finance calculator showing the monthly payment based on negotiated price, interest rate, down payment, etc.

I’ve done some research and have found that some banks will allow the seller finance portion from the seller to go towards the down payment of the loan, is that true?

Tenants in lower Classes will have lower credit scores, which means higher chance of defaulting on their lease payments.

Perhaps we "buy" the house from them for the $328K balance to satisfy the lender and don't need a large down payment and then have a separate contract with them to pay $x per month until we've paid the full $172K amount.