Most US embassies accept joint sponsors for fiancée visas. However, The US Embassy in Manila does not accept them for the K1 Fiancée visa. This policy has been in effect for the last 20 years. So, before you file for a K1 Fiancée visa, be sure that you meet the income requirements as shown on the form I-864P from the USCIS website.
If you are filing for a spouse IR or CR or I-130 alien relative petition, the Embassy will accept joint sponsors. It’s unfortunate that the embassy will not accept a sponsor for the K1 Fiancée visa, but the decision is strictly up to Embassy officials.
We have found that every single embassy and country has different rules, and it’s at their discretion.
The US Embassy actually requires you to meet the income requirements on your own, so if you cannot do that through employment, then you can possibly use assets in most cases, such as equity in your home, stocks and bonds, or cash deposits. The consular officer does not have to accept assets but usually does in most cases.