So are many of ours, so our hearts are heavy, and trying to come up with how you could make this work.
How long has he been with you at your mom's house, away from Grandpa's place?
Sometimes it can take several weeks, even months, for a chicken to adapt to its new place. Even though you're still with him, it's a whole new place with new strangers he's not used to.
So with that takes time and patience, yet, he's a danger to children and adults alike acting like this. He's probably a bit overwhelmed on top of everything else.
Just a suggestion: How about asking just one adult family member this week to help you and be his foster parent and have them talk to him when he's caged up when you're gone, leaving him in his cage though. Have everyone stay away from him but this one person. Then when you come home to take him out, have that person be with you. Have them hold him too and do everything you're doing, talking to him and each other in soft voices. Have that person feed him, give him a treat, and put him to bed at night while you are right there. Keep doing this together for several days. He will now see they aren't all enemies and may learn to trust the one as well as you. If that works, keep going while he gets to know each person in your house. I just wouldn't leave him out when there are children around though.
Don't trust him and be careful. If he's got sharp spurs, you can file the sharp tips with a heavy-duty fingernail file so they'd be dull.