Thinking of getting a broadband plan for my grandmother who is staying alone. Are there any senior plan?

For my mother, house no WiFi

Check out IMDA's Home Access and Mobile Access for Seniors programmes. These programmes typically apply to senior citizens who are already on financial aid.

Alternatively, if she does not use many devices at home, you can consider TPG's $5 Senior plan which offers 20GB of mobile data at 4G speeds, and unlimited data at throttled speeds.