While I feel completely for your sister, she faces a few obstacles, and I will point those out below.
"My sister's husband has asked for a divorce. My sister did not get mad or cause an arguement out of it and agreed that it would be best for them (he previously cheated on her and abused her). I am assuming that he did not expect her to agree with it and got upset (very childish). He is trying to do everything he can to make this a difficult process including taking their 1 year old son away and won't give him back."
Okay, his previous cheating and abuse are not going to be admissible at this point, unless she is claiming that it is CURRENT abuse that are the grounds for their split. They got back together, so his past indescretions are not admissable(sp?). As for him taking the child, since there is no order of custody, he has as much right to the child as she does. Not that what he is doing IS right, just that he is not breaking any laws by doing what he is doing.
"Would anyone be able to tell me what my sister's rights are? He is the parent that walked out of the relationship/family (is this not abandonment?)."
He didn't REALLY 'walk out', they both agreed that they should split up. He is simply the party that moved out of the residence. It is not even CLOSE to abandonment.
"To make matters worse and put my sister and all of us in the dark is the fact that his parents are both cops for the Missouri City police department in Texas. They seem to know all of the loopholes of the law."
He has used no loopholes, he simply moved faster than she did. Maury is right, she needs to get something legally started.
"My sister does not even have the car anymore. It was in his name and his mom was a co-signer on it. She picked it up one day and it is now parked at the Missouri City Police Department so that she cannot have access to it."
One of the downsides to not putting soemthing in both of their names. Sorry, sad as it is, there is not much she can do.
"Not only is this situation getting more and more complicated, I believe his mother is abusing her powers. I thought cops were here to protect our rights and not show others how to evade the law."
As I said below, he has broken, nor evaded, any laws.
"All my sister and all of us are worried about is whether or not he is going to give the baby back. The do have one other child (she is older - 3) and he keeps on driving by her house at all times of day in different cars (we think he may be wanting to snatch her up). We have tried talking to the local police deparment but they have told us that it is a civil matter and they could not help us. She would need to go to civil court and file for custody of the kids - etc. They also told her that if she does not do something soon that they could "lie" and say that my sister abandoned her son and that is why they have him."
First, you SEE him driving past in different cars, and do nothing about it? Step out in the street. Stand in front of the car. Videotape it, something. As for him claiming that SHE abandoned him, not gonna happen, as she is in the marital home.
The problem now is that you need money and an attorney to go to civil court, and my sister has neither. Can someone please help me and give me insight into help groups or information that may help us get the baby back. We don't want to wait too long because we fear that he may flee the state and we will never see the baby again
Why give a "senior" discount, they have had plenty of time to raise the money...