This is a great question because the DeLacy's do epitomize a romantic family in the literary sense.
Romantic literature is about the reality of things. With Romantic literature you will see things for what they are. In the case of the DeLacy's we do not see a family that lives in comfort and joy. What we see is a family who struggles because they are very poor. So poor, in fact, that even the monster feels sorry for them.We also know that the elder DeLacy is blind and whenever the younger DeLacys leave the house in order to, somehow make ends meet, there are plenty of tears. The nostalgic playing of old man DeLacy's guitar, the sad songs, and the pathos of the family is quite genuine. There is no "quick fix" solution for the DeLacy's: They just have to survive with what they have. This is what makes them a romantic ideal family.
They were not entirely happy. The young man and his companion often went apart, and appeared to weep. I saw no cause for their unhappiness; but I was deeply affected by it. If such lovely creatures were miserable, it was less strange that I, an imperfect and solitary being, should be wretched. Yet why were these gentle beings unhappy?
We know that the DeLacy's are also a united clan. They are united because they live in isolation, with little resources, and they are each other's main support systems.The fact that they live alone, and in what seems to be a run down place brings in the element of Gothic literature. Gothic literature is characterized by isolated settings, nostalgia, and for an ongoing problem in the lives of the characters. The DeLacy's problem is their poverty and their isolation. The addition of the creature lurking around and watching their every move adds to the macabre aspect of their lives.
Therefore, their current location and setting, their problems, and the fact that they cannot run away form their current sad situation is what makes the DeLacy's illustrate the Romantic and Gothic elements of literature in Frankenstein.