Why would the Philippines not allow a joint sponsor for a K-1?
Many US embassies accept joint sponsors for fiance visas. However, unfortunately, the most popular country for the K1 visa, the Philippines, doesn't allow them. They do allow joint sponsors for married couples applying for CR1 visas, but not the fiance visa. It's unfortunate, but it's at the discretion of the embassy and consular officers.
We have found with the over 180 countries that we work with, every single embassy and country has different rules, and it's at their discretion. The Philippines is one of a small number of embassies that do not accept joint sponsors for the K-1 fiance visa. They actually require you to meet the income requirements on your own, and if you cannot do that through employment, then you can also use assets in some cases. And even that falls to the discretion of the consular officer, as to whether or not they'll accept assets, and what type of assets they'll accept.