Thanks for sharing this, AtreyuFreak. I also have DID, and have very spotty memories of a lot of my past. I think this is somewhat "normal" for abuse survivors of all kinds, and particularly for those of us with DID. So you are not alone in experiencing this.
A lot of the memories that I have recovered were not necessarily experienced by me (Emma) but by one of my alters. Do you have good internal communication? I recommend you extend these questions to all (or some of) your selves, to work together towards answers, if this is possible for you.
It sounds like you do not wish to have contact with your brother (this is Michael?) and if he is not safe, then do not. However, if you feel safe to, you might look for some of the other children she babysat. You wouldn't have to be specific, you could just ask if they recall anything unusual happening when she sat for them. Please only consider doing this if it is safe to do so, I only suggest it if confirmation of events is very important to you.
I do not believe you are imagining things, trust yourself, trust your memories. And I certainly do not think you're an idiot! I think you are being very brave in searching through your past to find answers. I hope you will have an enlightening and safe journey.
Safest 's to you, and all within you!
~Emma