It looks like there might be a slight mix-up in your description. When referring to members of the string family, the hierarchy in terms of size typically goes from the smallest to the largest as follows:
- Violin (smallest)
- Viola
- Cello
- Double Bass (often simply called "bass," and is the largest string instrument)
So, the double bass is indeed the largest member of the string family. Each of these instruments has distinct roles in performance and contributes differently to the sound of an ensemble. If you have any more questions about string instruments or music in general, feel free to ask!