What are the basic differences between BTC ,LTC and BTG?

What are the basic differences between BTC ,LTC and BTG? What are the advantages and disadvantages of these basic differences? Do these disadvantages (advantages ) weaken (strengthen ) the basic principles of BLOCKCHAIN which we have belived in and excited (decentralization, Consensus Concept, low fees, high security , transparency …) ? i wish to get clear answers to these questions, especially from the members who have experienced the Bitcoin technology since its inception and They have knew the precise details of the conditions that led to appearance of LTC & BTG .