Hello K.,
Grandparent relationships with children are very special.
The information you provided is very interesting.
The Bipolar Disorder issue is very important and you will have to initiate a discussion with your Mother-in-Law and perhaps you can frame it as a legitimate inquiry into her ability to care for your children alone, given her tenuous heath realted issues.
But you need also take into consideration your bias against this woman that is rubbing off on your children.
I presume that this lady is your Husband's Mother and the Children's legitimate Grandmother or will be after your marriage.
There are very big differences in the actions in 2 year olds vs that of 4 year olds. Believe me, as a Grandmother myself, I can appreciate the difference. Four year olds can follow directions, commands and be helpful, while 2 year olds lack this ability. It can be very exhausting for older people to try to keep up with a two year old. Your Mother-in-Law may be waiting for him to attain the age and social skills necessary for her to be able to care for him alone.
You are wary of her because of her health related disability, yet you are failing to be understanding of her health-related disadvantages that may prevent her for caring for more than one of your young children at a time, which also stems from the same illness.
Elders with Bipolar Disorder may exhibit signs of nervousness and intolerance of the quick movements and inexhaustive bursts of energy that two year old's possess.
I just spent an entire week caring for 2 Grandson's ages 2 and 8 (because the youngest Grandson's other Grandmother died in a different State) and let me tell you, I have a husband helping me and we both ended the week needing a week to sleep off our exhaustion.
It was lovely taking care of them both. The 8 year old was very helpful in entertaining the younger child, but their activities had to be constantly supervised because of the age difference. We had to also keep our bathroom doors closed, we already had our house child-proofed (meds put away, no cleaners down low, plugs covered and on and on). Our two year old grandson still managed to open Grandma's Bottled Water when my back was turned and found a black marker inside my antique table and marked it up during the early A.M. hours silently and stealthily while everyone else was asleep.
Grandma was horrified! but I kept my cool, he was just leaving me some artwork! (LOL!). I can imagine if I had Bipolar Disorder how his unwelcomed foray into Furniture Decorating Art 101 might have sent to me stress level number 10!
Another thing that might set someone off is to have to encounter young people that don't seem to exert any control over their children in someone else's house. You didn't give any indication about why your Mother-in-Law might have "blown-up" but most times, something happened to make them blow and with Bipolar Disorder, they will often times be extra vigilant about watching for the recurrance of the unwanted behavior. Otherwise, you are talking about a Tourette's Syndrome type of behavior, wherein she may blurt out loudly, yell or curse.
People suffering from Bipolar Disorder are usually set off by events or actions.
K., please remember that 10 year olds are extremely perceptive. Your daughter can pick up on vibes of hesitation, reluctance, disgust, fright and a whole host of the range of emotions available to man. More than likely, her independence and unwillingness to hang around Grandma anymore than you like to, would naturally keep her from being Grandma's best buddy at this time.
The four year old is incapable of judging Grandma and very likely loves her unconditionally. However, you and she should reassure him that he will get to come visit again. Perhaps Grandma can help walk him to the Car and strap him in. Give him a kiss and tell him that she will see him on Saturday (or whenever you choose). This should minimize the crying episodes and separation anxiety.
If you all are going to be a family, you are going to have to open yourselves to acting like a family. Involve your husband in your concerns about his Mother. There are roles for everyone to fulfill.
I sense that since you have been the primary caretaker for your family that it is a little more difficult for you to now relax and allow others to assume their natural role as extended family members.
It is entirely possible that your Mother-in-Law is not intentionally trying to break up your family unit or to pick favorites. She may have simply grown an affinity to the only choice available to her. She has found someone who loves her unconditionally that she feels capable of caring for overnight, while you are trying to make her feel guilty for not being able to care for the other younger child that may be beyond her caring capabilities at this time.
Did she manage to raise your husband?
To that point, there is overwhelming evidence that suggests that many people inherit Bipolar Disorder and that there is a genetic vulnerability to developing the illness.
So I would suggest that you learn as much as you can about Bipolar Disorder so that you can begin to develop an enhanced understanding of your Mother-in-Laws challenges that will always be with her.
It would be such a shame to consider that your Mother-in-Law may have waited all her life for the joy of seeing her son marry the love of his life and acquire children in the process and that love would then consider wiping her Mother-in-Law out and alienating her from the son and his entire family because of a bias against an illness that she cannot change.
Good Luck!
Angie