Hi Kris,
You are likely reeling with the discovery that your sister is possibly a P. You are probably in a state of shock and disbelief and not quite certain of what you think you know. You have my sympathy.
"I feel relieved to know she has a reason for being so awful but am now completely overwhelmed with worry over her babies. "
That is a very relevant worry IF your sister is a P. You have made a tentative diagnosis based on your knowledge of her, but please be aware that that is all it can be - tentative.
"Is it possible for a P to have true love at least for their own kids?"
I suppose that it IS possible, but from what I know (I am NOT a doctor or therapist), not likely.
Many P's cannot abide babies or small children. Part of the reason appears to be that an adult P is totally and selfishly preoccupied with his/her self. A baby or a small child is equally preoccupied with his/her self - of course there are good reasons for this - for without it a baby or a small child would not survive. For a P, nothing exists except their own needs, wants and demands. A P is therefore unable to submerge his/her own needs, wants and demands, which is absoloutely necessary in order to lovingly and effctively care for a baby or a small child.
Since you are the parent of a baby, you probably have a good idea of what I am talking about. The baby does not care about whether you are sleep deprived, about to fall over from the Flu, or in need of a 10 minute shower. No, he requires your absolute attention whenever he is awake. The fact that you are tired, ill or unwashed doesn't concern the child in any way. He doesn't care!
A male P may view his child as a trophy, a 'thing' to be trotted out, when clean, fed and beautifully dressed, but otherwise not to be dealt with except when this 'thing' negatively affects the P, who will be impatient and maybe even act with rage against the 'thing', who dares to make demands on him. Demands, that a P does not have the emotional wherewithal to handle. A male P will leave all care to the mother. A female P cannot usually do that.
Is the father of your sister's children a caring individual? Is he a stable presence in the household? Is he involved with caring for the children? Are both grand-families lovingly involved with the children? Does your sister work, i.e., someone else takes care of the children during the day?
Please remember that caring for one baby or one small child is hard enough, while caring for twin babies must be a study in loving time management and herculian patience.
"Should I be concerned for my 6 month olds safety when she comes to visit? "
I would not leave her alone with the child. Nor would I use her as a babysitter even when the child is asleep. So long as you are present and paying attention that everything is as it should be, I don't see any reason to not have your sister visit your home. The only thing would be if she treats her own children in a bad way while your child is present. That could negatively affect your child.
Do you feel that your sister is less than caring, loving and patient with her children? If so, in what ways?
Take care and stay in touch,
Nan