can we use two 8gb memories to get 16GB Ram on MacBook pro 13inch mid 2012 model

Technically yes if you have two memory slots. But you need to be very specific about RAM choices with Crucial and OWC being two sources known to work. Their respective sites can lead you through the selection process.

Adding RAM can be helpful to certain apps, but if your expecting the added RAM to increase your overall Mac's performance, i.e. speed, that is not going to happen. Not to any meaningful degree anyway.