I agree with your brother and father that cryptocurrencies do appear to be a bubble but there is a difference. The price of these currencies will fluctuate - often wildly but it is because we are observing a change in technologies. When CD-Roms first entered the market they were around $5000. Families (in China) would buy many not because of speculation but what they represented. The CD-Roms meant an income flow and they started burning CD's for the pirate market. "Bitcoin" are the same thing, they are a new technology which are destined to change not only the way money works, but also the way that societies work.
Yes some of the major increase was due to Bitcoin Fever but also part of the increase is the recognition that it is an alternative. Ask your father if he believes the stock market will tank this year (it is within the last 3 years of the decade). Then ask him is the bond market is a good place to shift the money now. Finally ask if the commodity market is a good investment (it is in a longer range investment horizon). I think that more and more investors are dipping their toes in the cryptocurrency market as a desperation play in order to put their money into something that may have a potential. This is only a guess but I believe that Bitcoin will bounce one more time against the $12000ish support level and then resume its upward trajectory.
STEEM as an investment is totally different to Bitcoin. It is more than just a crypto ... it is "brainware". It is a community of over 500,000 exchanging ideas, goals and motivations. When the SMT technology drops, it will revolutionize a growing number of ways of communication.