As I said I don't know if they are Christians or not, I don't fully understand the Catholic faith so I wouldn't know if they are truly Christians or not.
Roman Catholics are Christian. It's really that simple.
The Christian religion is divided among different groups, the reasons for these many different divisions is a matter of often very long and complex history.
Broadly speaking Christians can be divided geographically, East and West. Eastern Christianity would include the Eastern Orthodox, Oriental Orthodox, and the Assyrian Church. These are the Christians of the Eastern Roman Empire (Constantinople, Jerusalem, Antioch, Alexandria, etc), the Middle East, Persia, and all the way to India. Western Christianity would include Roman Catholics, Protestants, the Anglican Communion, and the Old Catholic Churches.
Among these Protestantism is further divided into various traditions (Lutheran, Methodist, Baptist, Mennonite, Amish, Pentecostal, Reformed, etc) and usually then further sub-divided into denominations. The Southern Baptist Convention is a Baptist denomination. The Evangelical Lutheran Church in America is a Lutheran denomination. And so on.
So-called non-denominational churches are Protestant churches whose theological tradition is usually tied into the Neo-Evangelical and Charismatic movements of the 20th century; they are effectively single congregation denominations.
All the above are Christians.
-CryptoLutheran