hi bro,
many reefers who come to my house often question me why my tank is not in the hall but in my room. Me too face the same prob as you as my daddy dun really like the idea of having a tank in the house.
As for me, harmony is of great value and i sit down with them telling them that some of their views hurt me sometimes and i hope to get family support. Although they do not support me in term of financial and stuff like that, they stop their comment which is a millions improvement. And in time to come, when ur tank is up and ready, invite them to view ur marine creatures and appreciate the beauty of nature.
Do not fall out with your family. Communicate with them. Remember! Harmony is of great value. Cherish them and respect them so that they will respect you too. It;s not easy but perservere on k.