What is certain, data collecting tools from similar related research can be helpful; however, I personally believe that creating your own DC tools , and in your case an interview, is exhilarating and provides a satisfactory pay-off. First, you should find relevant theories pertinent to you research because the questions you are going to pose should be rooted in theories concerning caregiver phenomenon.Then, you should decide what type of interview you want to use: structured, semi-structured, and unstructured. Finally, you have to decide on the scoring grid by which you are going to weigh the responses produced by the targeted samples and the number of raters rating the interview. For more details, I refer you to Mackey and Gass (2005).
When employing research on areas like this dealing with facets of social action, employing a qualitative research paradigm is well suited to your needs. Especially since you want to begin without a necessarily well-formed initial hypothesis. While there are a number of qualitative research approaches that you can use, phenomenology may be best for your purposes. Your general question suggests that you may not be well versed in Qualitative research so I might give a bit more info than typical.
This suggested methodology (Phenomenology) can be used to investigate and analyze positive effects of being a caregiver by having people talk about their experiences as caregivers after the fact or as currently interpreted. We call that their lived experiences. They basically have constructed meaning as caregivers through their actions and interactions with others so by telling you their story from their point of view you can get a much better understanding of the phenomenon.
I think that Jonathan Smith has written some fine articles using phenomenology and what he (and others) refers to Interpretive Phenomenological Analysis. I have attached a few articles that he sent to me. He may be a member of researchgate...but I am not certain.
Grounded Theory would be another way to investigate this social phenomenon...but may involve more than interviews...refer to Kathy Charmaz' work in this regard...She is a member of researchgate.. Hopes this helps.