Here is an update....
On Thursday night after I found out that the order of protection was not granted, I sent STBX the following email:
It is unacceptable for you to call my mother, father, and sister to make threats to take DS by force or take one of [my sister's] children. That is completely unacceptable. You should not be contacting any member of my family to insult, threaten, or harass them.
The following statements you made to [my sister] this morning are threats:
"I'm tired of doing things the legal way. I'm going to take matters into my own hands."
"If anybody gets in our way, I'm gonna take them down."
"I'm gonna take one of your kids, so you can feel the pain."
My family is now in fear that you will carry out your threats. My parents no longer can extend an invitation to you to come to their home and therefore the visit for this weekend is cancelled. Do not come to their home. If you come the police will be called.
If you or your family have any questions please go through your attorney.
He replied that he didn't make those statements. I forwarded a copy of my email to my SIL and said, "FYI...I know you were planning on coming down here this weekend and you may not know what transpired today."
My SIL responded saying, "STBX told me what he believes he said. I know his brain does not interpret things accurately so I tend to think that the statements below are closer to accurate. In any case, I don't know what to do cause I have gifts for you & DS, and parents that are dying to see him."
The next morning SIL called me and we spoke for about an hour. I told her to please come and bring the inlaws, that they should come and see DS and still have their visit with him. I didn't realize this when I forwarded my message, but underneath my email was a string of emails with weeks of our emails back and forth. She could see that I've been asking STBX to come visit at my parents' house and also explaining the every other weekend visitation. She and I talked about a few things, I said, sometimes I want to call your brother, he used to be my best friend, I used to be the one who would reason with him about things. Sometimes I feel like calling him and saying, what are you doing? But I know I'll get the same guy who raged on my sister. I told her that his attorney is petitioning for me to pay the legal fees so he is thinking that a long drawn out case is great, cause I'll be the one paying for it. In the meantime, that's money that could go to our son. She said in her opinion, every other weekend is generous since STBX has NEVER kept DS overnight or even longer than 6 hours. I tried not to talk too much about our case, but it was good for her to see those emails to see that I haven't been keeping our son from him, but rather encouraging him to come visit since he will not agree on a temporary visitation schedule.
She said STBX doesn't share things with his family and they have no idea about what is going on. She said her parents are depressed and just wanted to see DS. So they decided to come without STBX. She said she asked her mom if she still wanted to come and her mom said, do you think it will make STBX mad? She told her mom, do you want to see DS or do you want to worry about making STBX mad?
SIL said that when she tried to talk to STBX about his behavior he lashed out at her too. She tried to tell him that this isn't a battle and he should put his weapons down. She asked him if his Lawyer is making him promises she can't keep (about 50/50 custody) and if their family isn't seeing DS in the meantime because of misguided legal advice. She tried to reason with him about "doing whatever it takes to see your son, and if seeing your son at your inlaw's house is what it takes then why can't you do that?" He told her she must be on my side. That she was using language that I use. That she must be talking to me. She said no, I'm not, I'm just telling you what is in the best interest of your son.
They came and got a hotel room to spend the night. My FIL does look pretty weak after his surgery and he has to use the bathroom every 45min or so. It was a very nice visit and they spent all of their time with DS playing with him, feeding him, holding him, etc. They brought us Christmas gifts from the family and it was touching to see how much DS means to them.
After seeing how hard it is for them to make the trip and realizing that this custody case could take forever, my mom and I decided to go back to my old town between Xmas and New Years so that they can have a visit with DS. Not sure how this is going to work with STBX but I'll have to ask my attorney for advice.