I became the owner of a joint checking account on my parent’s death. Am I required to share the account with my siblings?

No, the funds belong to you. Regardless of whether or not your parent intended for you to keep the funds, you are not required to share the funds with your siblings. Some children recognize that their parent did not intend for the funds to be kept by the surviving child and agree to share the funds with their siblings. If your parent’s intentions by adding your name to their account was solely to help them in paying their bills, it would be best if they named you as agent under a General Durable Power of Attorney and not as a joint owner.