if shares of stock were bought during a marriage and one spouse passes away, does the surviving spouse have to share proceeds with children?

Our mother married our stepfather 15 years ago. They had a joint checking account in which there was approximately 140,000. at our mothers passing. They had a combined income of approximately 5,286. per month in income. They moved to a retirement home in April of 2017; prior to that the home they lived in was paid for. The rent for their apartment was approximately 3600.00 per month. With the math of their combined income they should have had approximately made $950,000 over the 15 years of marriage. We know our step father bought CD's for his children and we also believe he bought stock during the marriage. Are we entitled to any of the checking account, CD's or the stock proceeds or any other money that was earned during their marriage? His children and our step father do not intend to share in this money and expect us to just go away. Our Mother did have a will that listed her three children as heirs to her estate.