Can My ex sisterinlaw's new husband make threats to my brother while he's in prison?

My little brother is in prison because he made some bad choices a while ago. His ex wife is probably the devil's right hand woman. no joke, she lied on him about multiple things including that he is a pedophile. NOT TRUE. he has two little girls and would do anything for them. he just doesn't like her. anyway he's been in prison sines june- on unrelated charges and he has got the help he needs to be a functioning person again. he is supposed to get out of prison soon and he promises to never make the mistakes he made again. he wants to see his girls and be the daddy to them that he never had. now the problem comes from where he is located. recently a new guard was igned to his cell block. this new guard is my brothers ex wife's new husband's cousin. now this wouldn't be a big deal except that my brother used the phone to call my mom as he always does, to inform her that this new guard had decided that he will make sure that my brother NEVER gets out and that "______ says hi." -i'm not writing her husband's name for obvious reasons. I know that his ex and her new husband set this up, but it's my word against theirs. i'm not just not a conspiracy weirdo the husband stated to me and my sister to tell my whole family " that - my brother- and our whole family will NEVER see the girls again and he will make sure of it. these people have been trying to defame my family's name for the longest time now and never stooped this low. other than the husband sent a petition door to door to convict my brother of pedophile. they have no grounds for these vicious lies. my brother was d by our father sinse he was 7 and from the age of 12 he was in and out of psychiatric hospitals. it took him years to overcome the abuse and then about 20 found his ex wife and married her. they had my niece shortly after. the relationship was rocky and then down hill. she is a liar and manipulator and he was no better. they should have just divorced, but didn't she just kept picking at everything and eventually he just snapped and that's when the abuse started. she egged him on so much. many times i broke up their fights. she would never leave him. then i get a call that she found child- on their computer. i think she planted it and she says she didn't. he leaves her and she loses it. soon after the "now" husband starts sleeping with her -while she's pregnant with my 2nd niece. she denies it and then my brother gets turned in for some non-related charges. the husband decides that he is guilty and she goes as far to naming the husband (not at the time tho) as the father on the birth certificate. she ends up going back to my brother while he is in treatment at a facility- the supposed pedophile. then she goes back to the now husband and has made my brother's and my family's life miserable. we moved on along time ago, but they continue this bull%&$#. we just want to see the girls. i practically raised the girls because she didn't want to be a mom. i love my nieces and miss them so much and my brother wants to be there for his daughters, but with this they're trying to destroy him. what can he do to get out of this? and can he get sent to another facility to get away from this instigator? is there anything that i can do on this end of things? and is this considered malicious harment? i know he's a convict, but everybody deserves a fighting chance. oh and if you think i'm just bitter because she's his ex, her and i used to best friends and my husband is best friends with the "now" husband. i need real answers please.