Okay. Do NOT let your sister-in-law kill them. She can be incarcerated for animal cruelty. Make her aware of that. Make a poster that says FREE kittens on it. Many people want kittens for their children or themselves. Thank you for caring.
You can also take them to the Balch Springs animal shelter on Hickory Tree, right next to the elementary school.
We are a spay neuter clinic so unfortunately we can not help you with that. You can reach out to Dallas Animal Services for assistance http://dallascityhall.com/departments/dallas-animal-services/Pages/default.aspx
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