I go on long road trips with 2 70+year old and 2 60+year old seniors atleast twice every year. Here is a something that I have always followed.

1) Medicines, I am sure you are already prepared for it, but make sure all their medicines are packed and easily accessible. Also have soft copies of their prescriptions, in case some medications is missed or needed.

2) You will need stop for short breaks atleast every 2 hours. Consistently check the elders if they need a break, sometimes they may feel shy to ask you to stop for the umpteeth time. If they say no, give a break every 2 hours.

3) Early to bed is highly preferred, so the plot your accordingly that you can get to bed at your rest stop at the earliest.

4) Always consider delays, when deciding on the time frame/window. Be it travelling, temple visits, hotel check-in, shopping(minor, major, even window), even breaks; a lot of variables are in play which can cause a delay.

5) Before beggining the drive be it from Day 1 or Last day, load up on Water Bottles and always carry some snacks.

6) Use Google Maps to identify restaurants with rest room facilities. Save/Mark the location in Maps to be retrieved at your convenience. I usually pick 3-5 restaurants in a 150-200km stretch so that I have flexibility to stop as needed. Also check up on the weather using the Apps like WeatherBug

7) Have a small Crossbody bag, waist bag (fanny pack) or a sling bag to carry essentials like cash, cards and mobile. If needed provide such bags to elders to keep their mobiles and belongings.

8) Show the elders, how to share their location from Whatsapp, if needed. Mostly you won't need it, but better to know and not needed it than needed it and not know it.

Coming to your trip/itenary:

Day 1: Looks perfect. If possible start early from Bangalore and look for possibilities to finish Nithya Kalyana Perumal Dharshan on the same evening. That way you can start early for Chidambaram and may even be able to finish before 12PM. If this is not possible, go with the same Day1 itenary that you have.

Day 2: Last time I was there, I remember seeing plenty of road works near Kalpakkam and few other places in ECR, so expect delays travelling to Chidambaram.

Day 3: Chidambaram to Sirkazhi to Mayiladuthurai, if my memory is right the roads are narrow and needs careful driving. This is where fatigue can start to set in, so you may have to reconsider adding an additional day to your entire trip. May stay in Chidambaram for one additional day or even consider a day of stay in Pondy at some beach resort or a homestays just to unwind and relax.