Hi!
For plaque- no home remedy. Do a professional scaling done once in 6 months and after that procedure home care of twice brushing, flossing and rinsing after each meal - every day will help.
Tooth cavities definitely have to go for treatment by removal of the decay part and filling it back with cement!
Next Steps
Visit a dentist for the further procedure.
Health Tips
Treat the teeth at the earliest and don't delay before the condition worsens. Take care.