Dear sir, As u mentioned, the below is our proposed route.
Trivandrum - Madurai - Bangalore - Pune - Mumbai - ?? - Himachal ?? - Delhi - Agra (?) - Jhansi - Nagpur - Hyderabad - Bangalore - Madurai - Trivandrum.
We may be advised a better route. Our aim is to travel through Maharashtra (Lonavala), Rajasthan (to visit major tourist place only), Punjab and then to Manali.
We are planning to return through Delhi-Agra.
Pls send ur valuable suggestions
You may do Trivandrum - Madurai - Bangalore - Pune - Thane. Between Pune and Thane you can cover Lonavala.
From Thane you can join NH3 (Bombay Agra road) by going through Thane - Nashik - Sendhwa - Manpur - Ratlam. Now from Ratlam either yo decide to enter Rajasthan via Chittorgarh or Udaipur. You can cover Chittorgarh, Udaipur, Jodhpur, Ajmer, Bikaner on your way. Once in Bikaner then you can enter Punjab via Ganganagar.
From Punjab you can come towards Delhi by covering Kurukshetra, Panipat, Sonipat. From here you can come to Noida and proceed towards Agra covering Mathura on the way.
From Agra you can move towards Jaipur. After covering Jaipur you can go to Sawai Madhopur. From here either you can take back Chittorgarh route towards Mumbai or Indore route towards Mumbai. Please don't go by Gwalior - Jhansi route as roads between Agra and Gwalior are good but once you cross Gwalior then you will come across road widening work with lot of diversion, dust and slow moving trucks.
From Mumbai to can go back to Trivandrum via Bangalore - Madurai.
You need to decide on places (attraction) you want to cover in these route. Based on this you need to plan your days, stopovers and route.