Salam
Don't sell a good car.
Two older cars would increase maintenance (minor and major) and fuel cost.
A practical solution would be to set aside budget for Uber/careem/yango services.
You can also just hire a driver who can drive around anyone whenever the need comes. For example if two of the 6 members go to school/university and two others to work the driver can drop all of them off and come back home to make the car available for use of the two people back home.
My point is you can plan things in a way that you get around the problem. Do a cost benefit analysis.
And if you think you can manage with one car then do that and in the meanwhile save up money for a second car.