We are having difficulty locating the web site. As far as I can see, there is no church registered as "Reformed Church of God" anywhere on the web
I rather suspect that they are an offshoot of the Armstrong original which was called "The Worldwide Church Of God" When He died a great deal of controversy swerled around his beliefs and the way he was viewed by the members. Rumors even began to circulate about certain sexual improprieties between him and a daughter.
He had for instance dictated that no divorce and remarriage was permissable in his group, yet he indulged his son's misconduct for a while, and evetually himself remarried.
When he died his own church became mainstream, dropping some of his more extreme beliefs, such as British-Israelism, maintaing all the Jewish feasts such as Passover, Day of Atonement, etc and including many of his racist views as well.
Several offshoots then developed each appending the expression "Church of God" to their name. To the best of my knowledge these were:
Global Church of God
Philadelphia Church of God
Living Church of God
Church Of God, Reformed Tradition
If the group you are referring to is one of these then they will believe a variation of Armstrong tradition: 1 The British Race is the "Spiritual Israel" of the NT 2 Soul Sleep 3 The destiny of the believer is to become God.[similar though not the same as Mormon belief] 4 Sabbath keeping 5 Jewish diettary laws to be kept 6Herbert W Armstrong was the final messenger of God 7 The "Born Again" experience occurs only at the resurrection 8 "God" is a family presently consisting of The Father and Christ, but soon will constitute all the believers in Armstronism 9 The British Monarchy is directly descended fro the Jewish line of David 10 The OT god is referred to as JHVH, and is identified with Jesus Christ in His Pre-incarnate exixtence 11 The 10 Lost Tribes Of Israel were regathered by God to form the various nations of Europe. 12 Ephraim/ Manasseh for instance are Britian/America 13 Before Adam was created, the earth was the home of a race of angelic beings, who eventually rebelled against God, and because they were expelled, Man inherited the earth as a dwelling [This is explained as part of a "Gap Theory" in Gen 1:1] 14 Christmas and Easter are "pagan" in origin, we need to observe the Jewish Passover, Day of Atonement, The Feast Of Pentecost etc 15 Physical healing is a spiritual, not medical process
The different groups have played around with these teachings, dropping some, modifying others. Some have adopted the Trinity, some not. Some have dropped Br Israelism, and some have even acquired certain Charasmatic traits.