Re: Can each couple who share a 1.4 million mortgage deduct mortgage interest on 750,000 or is 750,000 the limit of the loan?

Can you clarify....is this 2 unmarried individuals that share ownership of a residence? Or a married couple that are filing married/separate? 

The "each couple" part is confusing.

Can "each couple" means it is 4 people, two married persons, such as sharing a lake cabin and splitting the debt? Whose name is on the mortgage? Who is making the payments? For instance, older parents and their married adult child and spouse?

Yes, two married couples who are all on the deed and the loan.

For your question as to what this is based on: "You can deduct home mortgage interest on the first $750,000 ($375,000 if married filing separately) of indebtedness. However, higher limitations ($1 million ($500,000 if married filing separately)) apply if you are deducting mortgage interest from indebtedness incurred before December 16, 2017."

From here:

https://www.irs.gov/publications/p936

But you cannot go to $750,000 each. Half of $1.4 m is only $700,000 each.