Each Azure subscription can contain multiple account administrators is incorrect. While an Azure subscription can have multiple administrators through RBAC roles, there can only be one account administrator per subscription.
Each Azure subscription can be managed by using a Microsoft account only is incorrect. Azure subscriptions can be managed using Microsoft accounts (MSAs) or work/school accounts (Azure AD accounts).
An Azure resource group contains multiple Azure subscriptions is incorrect. The hierarchy is reversed - subscriptions contain resource groups, not the other way around. Resource groups are used to organize resources within a subscription.