Wow, if they claim to be the real Catholic Church, where were they for these 2000 years.
I would like to underline two topics from the website you posted, about Thorah and Sabbath. The Thorah at that time had been added/altered by the pharisees for their own political purposes. The Thorah according to them, was far from the love of God originally meant to be. Paul in his letter to the Roman contradicted the thorah and the law of love from Christ, by no mean that Paul abandoned Thorah entirely. In his letter, Paul meant that the Thorah in the form that the Jews observed during that time was not absolute, as the soul of the Thorah was betrayed by additions and substractions by the pharisees at that time. The original value of the Thorah is still valid even until now. Jesus himself said that He would not erased the Thorah even an iota. What He meant definitely was the original Thorah.
We go to the Church on Sunday because God himself told us in the book of Revelation (Rev 1:9-10). The Day of the Lord used to be the day that the early Christian assembled together weekly (1 Cor 16:2, Acts 20:7). At that time, they could not possibly assembled together to discuss Jesus’ teaching in the sinagoges. So, they must did so outside the sinagoge. Definitely, they could not assembled together on Sabbath due to the ban to travel during Sabbath. So, this assembling date of the early Christian could not be the day of Sabbath. Secondly, Christ was risen definitely on Sunday. Remember that He died in a day prior to Sabbath, and risen on the third day. In the Jewish calendar the rising day of Christ has to be Sunday. So, since we are Christian (not Jewish as a religion), we assemble together discussing the teaching of Jesus on the Day of the Lord, which is Sunday. In this case, let the Jewish observe Sabbath, and let us observe the Day of the Lord. Jesus, as well as His deciples and even Paul observed Sabbath because they were Jews. They were still bound by their heritage by birth. Remember, Jesus is the Lord of Sabbath.
If one is seeking the Church that Jesus built, seek no further. Visit this website often, and you will find the answer. We are Catholics following Jesus based on the 7 sacraments, and acknowledging the apostolic teaching from Peter until his latest successor today, in an unbroken chain.