1. I take sugar in my coffee. (sometimes) - Correct
2. Ramon and Frank are hungry. (often) - Correct
3. My grandmother goes for a walk in the evening. (always) - This could be rephrased for more natural language. Perhaps: "My grandmother always goes for a walk in the evening"  or "Every evening, my grandmother goes for a walk."
4. Walter helps his father in the kitchen. (usually) - Correct
5. They watch TV in the afternoon. (never) - Correct
6. Christine smokes. (never) - Correct
7. They are happy. (always) - This sentence is a bit awkward. It's more natural to say "They are always happy" or "They're always happy."  However, "always" might be a strong word for happiness.  Consider using "often" or "usually" for a more realistic portrayal.
8. You study for the exam. (rarely) - Correct
9. She doesn't help her mother. (often) - Correct (This implies she helps infrequently)

6. Ramon and Frank are hungry. 

=> Ramon and Frank are often hungry.

7. My grandmother goes for a walk in the evening. 

=> My grandmother always goes for a walk in the evening.

8. Walter helps his father in the kitchen. 

=> Walter usually helps his father in the kitchen.

9. They watch TV in the afternoon. 

=> They never watch TV in the afternoon.

10. Christine smokes. 

=> Christine never smokes.