How to organize the Model class in Asp.net web api core 6?

I am to make re use the variables, without creating new variables and class everytime.

For example,

I have UserAuthentication Api controller

public class AuthController : ControllerBase
{
    [HttpPost("register")]
    public async Task<ActionResult<UserAuth>> Register(UserRegister registerRequest)
    {
        //....
    }


    [HttpPost("Login")]
    public async Task<ActionResult<string>> Login(UserLogin loginRequest)
    {
        //....
    }
}

I created Model class like be below

namespace DemoAsp.Models.User
{
    public class UserLogin
    {
        public string Username { get; set; } = string.Empty;
        public string Password { get; set; } = string.Empty;

    }
    public class UserRegister : UserLogin
    {
        // I will use the Variable Username and Password from base class "UserLogin"

        public string FirstName { get; set; } = string.Empty;
        public string LastName { get; set; } = string.Empty;
        public string Email { get; set; } = string.Empty;
        public string ConfirmPassword { get; set; } = string.Empty;
    }
    public class UserData : UserRegister
    {
        // I will use the all the Variables from both class "UserLogin" and "UserRegister", In case I need it.
    }

}

I don't think this is the way to organize the MODEL Class and their fields. If I define the variable separately for UserRegister and UserLogin, then the variable name will be repeat

Could someone suggest me the way to handle/organize the Model class.

So that it will be helpful to create and maintain any other models