Hardik Dhaduk wrote:what would be your recommendation to account for any seismic events and lateral forces exerted by the roof?
You should talk to a structural engineer in the area where the house is located.
Western Gujarat has highest seismicity in India. On the other hand, the house is still standing and seems fine (except the termite affected roof). Seismic retrofitting can be more or less intrusive. It would not make sense to surround an old house with concrete beams, but since you are already considering the roof replacement - a good concrete bond beam will help. It holds the walls together and resists expanding forces exerted by the gable/hip roof.
Since you want to convert the building to a livable house it would make sense to build walls inside in such a way that they will be perpendicular to the long walls and spaced 3-4 m apart. They will brace the long walls, reinforcing them. Then a continuous bond beam can be poured over all exterior and interior walls (I did it for my house). It's possible that the fact that the walls are 450-600 mm, helped to survive quakes in the past. Building with thick/low walls are more resistant than thin and tall. Because of that I would recommend to build the interior walls at least 400 mm thick - they would look compatible with the old building and would also have comparable mass to the exterior walls.