My sister's 11-year-old son has a lot of emotional problems. He's shown the ability to act violently against others. He's attacked people - even teachers - with sharp objects. He's also tried to commit suicide more than once. All sorts of state agencies have gotten involved, including the state's child welfare agency.
My sister has issues, too, so there are real questions about whether she can provide a stable home for him.
The problem is his father. He's a hard-core gun humper. He evidently got into some trouble with child welfare when he claimed he didn't have any loaded guns in the house, only to later admit he wasn't counting the handguns, including the 9mm he sometimes carries on his hip. I have no idea whether they're locked away, but I tend to doubt it. This should disqualify him from being the custodial parent, in my opinion.
There comes a point at which one's right to bear arms should give way to the right of everyone else to not get shot.
(As for my nephew - my wife and I discussed, VERY briefly, whether we'd take him in should his mom and dad not be able to keep custody. Neither of us wants him in foster care. But that discussion ended swiftly - no matter how much I love my nephew, our first priority is our 5-year-old daughter. It's just too much of a risk.)