What a horrible thing to experience! My heart goes out to you. Just by the nature of what you've related about Megan's background and her many "runaways", it would seem that HER family would be more closely scrutinized for a guardianship issue.
This is just off the top of my old head, but it would seem as if there WAS this past history under her parent's roof, that documenting this, or finding people that would be willing to swear that she was miserable as a child (more than the usual teenager,lol), that gathering "evidence" like this would help to further your cause. Did Megan have girlfriends she confided in that might help to prove what unfit guardians these grandparents would be?
There ARE some very strange and "I don't BELIEVE it" cases out there. I went to a meeting last Tuesday night for FADD (Families with Attention Deficit Disorder) because the grandson WE are raising has Asperger's Syndrome and has Attention Deficit Hyperactive Disorder (ADHD) and there were two newcomers to the group. Both were grammas like me, but the experiences THEY shared were startling....much like yours, except for the remaining "parent", the Dad, in both cases, WAS a jerk, ( the Moms had also committed suicide) and these grammas have gone through hoops to get legal custody of their grandkids. It's amazing how ridiculous the legal system is in this upstate NY county, and will shift the kids from foster home to foster home when they have willing, able and loving grandparents who are capable of giving the kids homes AND have the blood relationship continuance. I assume that other counties have much the same flaws and ridiculous policies.
So you really need to "do your homework" and pull up EVERY bit of favorable and positive (for the courts) information you CAN, and don't waste a moment doing that. I don't want to drown you in cold water by sounding so negative, Larry, but the Family Court System can totally surprise you by some very strange reasonings and stupid decisions. When we hear about these things, we sit back with our mouths open and say "how COULD they?", and we don't KNOW...but they DID, and they DO, so try and keep one step ahead of them and consider all the stops that the courts might pull out in favor of Megan's father.
ONE very good thing in your favor---the Watchtower Society is coming under a LOT of criticism lately in the media (and they deserve all that and MORE), so their image of looking "squeaky clean" has been smeared, which can only help you :o)
Their shunning, their forcing children to live abnormal childhoods by not celebrating any holidays or attending school functions because ALL nonJW kids are BAD association....the whole nine yards and lists of what a JW kid can't do.....are good "starters", along with the no-blood issue and the pedophile problem should be mentioned to the courts as well. These are the things that children CAN and HAVE BEEN subjected to under the care of JWs. Use all the ammunition you can---THEY will.
You need ALL the support you can get right now, on a local level. You have lots of emotional support right here....and several folks here have great advice and know who to contact and where to obtain helpful reading material for situations like yours. This IS a "winnable" (is that a word?) case, but you need to dig in your heels and legally fight this.
Please keep in touch here on JWD, and let us know if we can help somehow, and let us know how things are progressing. We CARE.
Hugs and Good Luck,