In regards specifically if you don't have any positive relationships with relatives yourself to draw from. I'm assuming writing only about characters who have negative familial experiences would become one-note rather quickly.
- Watch movies and read books that have positive family interactions.
- Hang out with friends who have have positive relationships with their family.
Also note that family relationships don't have to be viewed as simply "good" or "bad." Flanner O Connor's complete short stories is a great resource for complicated family relationships. Her stories are in particular about Southern characters.
Always try to write from personal experience first, because it's your richest source of detail. If your personal experiences aren't giving you what you need, copy authors that do what you think is a good example of it. Obviously you'll need to eventually graduate from copying others, but when you're learning something new, imitating somebody who does it well is how you build good habits and learn the technique.
It might help to think more deeply about the subject, rather than reducing it to simple good/bad dichotomy. Find specific qualities you think are positive about a family relationship (i.e. supportiveness, communicativeness, unconditional love, etc) and look at how different authors portray these.
Alternatively, you can use the inverse of your own experiences. You have bad experiences, so in other words, you know what a good relationship is not. Think about a hypothetical family that was the opposite, or merely very different from your own experience. Think in terms of specific examples to real life examples you have.
Think about how you interact with your family. Often there is the some niggle between siblings, some lovey doveyness between the parents, and the annoying grandma, (can't have a good story without the annoying grandma; she causes conflict within he family). Depending on the relationship between the family, often means how they act towards each other. I hope that answers your question. (P.S don't change your whole book, just so there is the annoying grandma. She is not compulsory. I just find it fun the write about annoying grandma's). 😀