My Mom died and left 100 shares of just one stock. As personal representative of her estate I was told I have to open an estate account before they can split the stock between me and my sister. But some of the things they are asking on the form make me very uncomfortable, such as my net worth, liquid assets, tax bracket, etc. I didn't even give this information to my probate lawyer, nor was I asked. Neither my sister or I want to be active traders- she wants to cash hers in, and I want to just keep mine, that's all. Am I required to give them this information, or am I just being sensitive? Thanks for any help on this!

No you don't, they are setting you up to try to sell to you, marketing info.
Have your attorney contact them, or merely tell them no, and your attorney will be in touch of there is a problem.