Hello Sir,
-There would be capital gain of around Rs. 8 lakh on flat no 1 sales.
-There would be capital gain of around Rs. 12 lakh on flat no 2 sales.
As you have already invested 12 lakh in tax free 54EC REC bond on 07.10.2019 So you will get full capital gain exemption on flat no 1.
Now you need to pay the taxes on sales of flat no 2 only i.e. you will be required to pay the capital gain tax@ 20% (plus applicable surcharge & cess) on capital gain amount of Rs 12 lakh.
Please take a phone consultation for better understanding.