I'm so sorry you are going through this. Children need equal love and attention from grandparents.
I believe your MIL is highly manipulative and has been doing this for a life time, so it won't suddenly disappear no matter what you may say to her. In fact, I believe your DH's behavior suggests he was thoroughly manipulated as a child by her in many ways and now can't even deal with it. (As someone else may have suggested.) Also, you were under no obligation to have her at the birth, so I suppose I disagree with the idea that you need to apologize to her about anything concerning that issue. This would only enable her. Not to mention there are plenty of parents and grandparents out there that have strong bonds with their children and grand children who weren't at the birth. For instance, talk to some adoptive parents or even other grandparents who were living too far to even be around the birth. So this really is an excuse on her part as to why she gets to treat DD2 differently. Also, no matter what type of bond she has decided to have with your oldest she doesn't have the right to anything that is destructive and unhealthy to your family. You need to limit your contact with this person and make sure she is not alone with the children ever.
Unfortunately, the cold reality is that you have to take steps to protect your family immediately, because reasoning is not enough with this person.
As someone mentioned, codependency, but even perhaps something like Narcissistic Personality Disorder, etc... Your husband may need some help dealing with this too.
However you choose to deal with this I truly feel for your difficult situation.
I believe your MIL is highly manipulative and has been doing this for a life time, so it won't suddenly disappear no matter what you may say to her. In fact, I believe your DH's behavior suggests he was thoroughly manipulated as a child by her in many ways and now can't even deal with it. (As someone else may have suggested.) Also, you were under no obligation to have her at the birth, so I suppose I disagree with the idea that you need to apologize to her about anything concerning that issue. This would only enable her. Not to mention there are plenty of parents and grandparents out there that have strong bonds with their children and grand children who weren't at the birth. For instance, talk to some adoptive parents or even other grandparents who were living too far to even be around the birth. So this really is an excuse on her part as to why she gets to treat DD2 differently. Also, no matter what type of bond she has decided to have with your oldest she doesn't have the right to anything that is destructive and unhealthy to your family. You need to limit your contact with this person and make sure she is not alone with the children ever.
Unfortunately, the cold reality is that you have to take steps to protect your family immediately, because reasoning is not enough with this person.
As someone mentioned, codependency, but even perhaps something like Narcissistic Personality Disorder, etc... Your husband may need some help dealing with this too.
However you choose to deal with this I truly feel for your difficult situation.
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