This sounds too me like they don’t understand how Amazon works. There is no reason to have different sellers to cover different regions because Amazon will distribute the product to their warehouses across the country.
In addition, the number of sellers selling a brand is not important for marketing. It is in fact easier with one seller because you can trust all of your data more and do not have to coordinate with other sellers on campaigns.
What I am much more concerned about is the opportunity. Are they asking you to invest $60,000 in a product that has never been on Amazon? It sounds like the brand is new to market and they have immediate sales expectations. There should be zero expectations. There can be no guarantee of success with a brand new product.
It also sounds like they have money problems which seems like a red flag to me.