My Mother Just Passed Away.

My mom passed away on Friday night. I'm still unsure what exactly she left anyone because she didn't have a will. I was told I'm the beneficiary of her bank account though. When my grandfather passed away 4 years ago he had a retirement account through amstead that both my mother and my uncle were beneficiaries of. I don't think my mother ever listed anyone as a beneficiary of her portion of it, so I'm afraid the money won't be able to be passed down and will default back to the company. However, that's not why I'm writing this. My mother had been in bad health for awhile, and she was rushed to the ER a month or so ago and had a heart attack and multiple heart surgeries. I'm not sure how much it accounted to, but she was told it was around $300,000 at some point. My question is am I going to be responsible for that money? My brother currently lives in the house she had recently bought for $187,000 and she had a brand new car that she paid $60,000 for. I'm not sure how much money is in her accounts, but I know it's not $300,000 and I'm definitely able to pay that. Am I going to be held responsible or are we going to have to sell her house and car to help pay everything off? We live in Henry county in Missouri if that helps at all.