It could be covid, don't take any chance and get her tested as soon as possible, if she cannot leave then ask some near by laboratory if they can come to your place or book online, whichever is earliest and suitable to your situation, and isolate yourself in another room from them, if you frequently go out as they are vulnerable due to age and take good care of them like maintain their hydration, asking them to wear double surgical mask and you should also wear double mask, it has a huge role in the percentage of transmission of virus. Try to keep them warm by room heater, giving kadha with ginger, tulsi leaves, bay leaves, pepper, cardomom, turmeric powder.
For some more home remedies, you can consult me privately here on practo and for any further queries and medication regarding covid if they come out positive( which I hope they don't) you can contact me here on practo or privately on my number 8895_9099_75
Next Steps
get your parents and yourself tested at the earliest.