Hi Meisam, The context of the sentence will dictate which word you use. Big is a mainly informal adjective, whereas large is more formal. Large is generally used for countable items, so in your example we would use 'large family' in writing (although in informal speech you might choose to use the word 'big'). Note that context is important... nobody would be happy about buying an item of clothing that was labelled 'big' as it has a negative connotation in this context. However, it is generally considered positive to describe somebody as having a 'big heart' (which suggests that they are kind/considerate/empathetic). Please feel free to contact me if you need any further assistance with this :-)

No, but you don't need the capital "B".