My sister is a terrible mother and, because of how she treats her children, I'm thinking about speaking up in court on my brother-in-law's behalf but am worried about the repercussions. Everyone in my family is aware that my sister has passed the kids on to anyone who would take them, so she could go out drinking with the girls, and has openly said she never wanted to be a mother in the first place. Beyond the partying and lack of paternal instincts, she struggles with mood swings and depression and, on many occasions, didn't even get out of bed which meant the kids had to fend for themselves and they're only 5 and 7. Obviously my brother-in-law should get full custody but I'm worried about the war I'll start if I speak up against her in court.
Considering the welfare of two small children is at stake, you can't worry about what may or may not happen once you've told the truth in court. Your sister sounds mentally unstable to me, to the point where she needs counseling and medication, and until she gets help she's not only a bad parent but she's a danger to her children. Speak up for the kids in court, and see to it that they're in a loving and safe home. Then, get the rest of the family to encourage your sister to get help. Once she's well, she could always go back to court and try to regain custody- if she so chooses.
Keep me posted,