Spending a night at Pang is a bad idea, since it is at higher altitude than Sarchu. Also at least last year, motorcycles rented from outside Leh weren’t permitted on the tourist circuit i.e. after reaching Leh, you had to hire another motorcycle from local rental companies for Khardung La and Pangong Tso.
You can hire motorcycles from Manali and drop them in Srinagar, though expect to pay anywhere from 7-10k per motorcycle for it, along with Rs. 800 to Rs. 1700 per day rental.
Indians no longer need permit to visit Khardung La and Pangong Tso.
My advice to you would be to fly directly to Srinagar, visit Leh and then ride to Manali, drop the bikes there (which you will rent from Leh) and then take train/flight back to Chennai. This will free up at least 3 days, which you can spend in Ladakh. Plus you don’t want to be in Kashmir around Independence Day, very tight security and high chance of terrorist attacks and/or bandhs.
Road for most part are a mix of good and bad, nothing as bad as the Losar - Gramphoo stretch though.
For pillions it would of course would be a tiring ride.
Also keep in mind that you will be traveling in monsoon season, so expect rain and landslides till Baralacha La on Manali side and till Zoji La on Srinagar side.