I think you must keep the sleeper ticket and cancel 2AC.

If it is Mangala and you are boarding at Kalyan, you should first check which type of quota it is as Kalyan is an intermediate station

We have E tickets, so basically if our tickets (ie both ac and non ac ) does not get confirmed then we cant board the Train? Also we dont need to cancel right coz it will automatically get canceled?

What is a quota? what are the chances of getting Tatkal tickets

no

Sir, boarding the train with Wait listed E ticket is not allowed. If both your tickets remain wait listed, then you cannot board the train. You don't need to cancel in case it remains wait listed after chart preparation. Money will automatically refunded, deducting some service charges. But after chart preparation, if both of them get confirmed, then you cannot cancel one of them. This is the reason why everyone said to keep the SL ticket and cancel the 2AC ticket, as seats are very high in SL as compared to 2AC

Sir, today was the date of booking tatkal tickets. But now the status is Regret, which means that you cannot book tickets in tatkal.

someone else can provide you more information on quota. In simple lamguage the WL in Kalyan for Mangala is against the number of berths marked for Kalyan. Therefore, the waiting list at Kalyan is far more difficult to get than in Delhi. So waiting list 26/27 is easier to clear at DElhi than in Kalyan. I am sure someone else will give a better explanation

correct. good example

We have to go to Cochin, can you please recommend the best way to get there incase our tickets dont get confirmed? maybe some other city we could go to and travel from there.