Hello and thank you for entrusting me to assist you. I am very sorry to hear about your husband's heart condition and the difficult time you are now having with your employer.
Unfortunately, what your employer is doing is legal. In fact, not only is it legal but they are actually required by law to designate the leave as FMLA. That may sound strange to you, but let me explain.
FMLA and vacation days serve completely different purposes. Vacation days are simply a form of wage replacement when an employee misses work. They do nothing to actually protect an employee's job. An employee can have 100 vacation days and be terminated on the first day they take vacation. Using vacation days does not keep your job secure.
FMLA, on the other hand, exists for the SOLE purpose of protecting an employee's job. FMLA has nothing to do with wage replacement, but very often FMLA is taken at the same time as "vacation days" as one protects the employee's job while the other ensures the employee gets paid.
So, FMLA is what is protecting you here, not the fact you have vacation days. So, to insist that your leave not be designated as FMLA would be to insist that you don't want the law to protect you. It is a self-defeating position, and for this reason isn't even allowed. The FMLA actually REQUIRES employers to designate qualifying leave as FMLA--otherwise, they could convince an employee they didn't "need" their FMLA leave and then terminate them because the only law that protected the employee (FMLA) was not in effect. That would be an absurd result that would render the FMLA meaningless.
In short, your employer can require you to take FMLA. I cannot speak to instances in which employees were not required to take FMLA under similar circumstances (it may be that the employee's did not qualify for FMLA protection as there are very stringent requirements for the law to apply) but in any case, your employer's failure to abide by the law there does not change your situation here.
I hope that you find this information helpful. Please do not hesitate to let me know if you have any questions or concerns regarding the above and I will be more than happy to assist you further.
If you do not require any further assistance, please be so kind as to provide a positive rating of my service so that I may receive credit for assisting you. Very best wishes moving forward.