My Mother is playing huge games between me and my siblings. Is this part of dementia?

IMHO, yes, this could be part of the "covering up" part of dementia. My father never wanted all 4 of us to talk to each other. In fact, if it happened that 2 of us were together, we had to be talking to him, going with him, talking about him, watching his tv show, etc. He could not tolerate us going out in the yard or another room and having our own conversation. My father likes to trash talk about each one of us to the others - heaven help us if we came clean to each other about what has been said.

My point is it could be a kind of paranoia and fear that all the kids may compare notes, get on the same page, discuss - openly and honestly - what can and should happen. (loss of control).

For me, once all of us got together....we had not been all together for almost 7 years....we all forgave each other of a lot of baggage that was carried around, much perpetuated by the father.

My rambling point is this: I encourage you to reach out to siblings, make sure everyone knows everything and make a point to get together, even with a conference call or group email so that you have the opportunity to get on the same page as to the health, condition and outlook for your parent.

I have found that even with seniors who don't have dementia, the facts can often be distorted. I have learned to independently check behind their backs, because they forget, are confused or somehow do not relay the information correctly. Their intentions are good, but they just don't get things straight anymore.

There is an easy way around this. You can talk right to the siblings so you'll know what each other is doing. Problem solved. I don't know why your mother is not telling you. It may slip her mind or she may want to keep you separate for some reason. You can work around that by talking to each other.

I wish I knew the answer to your question but I will say that it may be part of dementia because my mother-in-law did the same with us. We lived out of town and only made the visit once a year. My husbands brother and sister lived within a short distance from the mother) Never, never were they told until after we had gone. My sister-in-law was puzzled saying "Mother never tells me that you are coming."

Why do you think she is lying to you? Why would she keep you from your siblings or relatives?

When my BIL and SIL came into town, they were busy with staying with each set of parents. We didn't get much time together so we started emailing beforehand and arranging dates for dinner together, shopping trips etc. Then when they got to town, it was all set and went smoothly.