What to say about the Sabbath to Sabbatarians?

Question:

I have a few Sabbatarian (SDA) inlaws (Aunts inlaws) and they know my extreme intrest in catholism are really pounding me on this and I would like to know what would be the wisest thing to say and the best way to presesnt this to them?

Since they have great distrust for the teachings of the Catholic Church, you might consider discussing this by quoting from Jewish scholarship:

The origin of the Sabbath, as well as the true meaning of the name, is uncertain. The earliest Biblical passages which mention it (Ex. xx. 10, xxxiv. 21; Deut. v. 14; Amos viii. 5) presuppose its previous existence, and analysis of all the references to it in the canon makes it plain that its observance was
neither general nor altogether spontaneous in either pre-exilic or post-exilic Israel. It was probably originally connected in some manner with the cult of the moon, as indeed is suggested by the frequent mention of Sabbath and New-Moon festivals in the same sentence (Isa. i. 13; Amos viii. 5; H Kings iv. 23). The old Semites worshiped the moon and the stars (Hommel, "Der Gestirndienst der Alten Araber"). Nomads and shepherds, they regarded the night as benevolent, the day with its withering heat as malevolent. In this way the moon ("Sinai" = "moon ["sin"] mountain") became central in their pantheon. The moon, however, has four phases in approximately 28 days, and it seemingly comes to a standstill every seven days. Days on which the deity rested were considered taboo, or ill-omened. New work could not be begun, nor unfinished work continued, on such days. The original meaning of "Shabbat" conveys this idea (the derivation from "sheba'" is entirely untenable). ... The Sabbath depending, in Israel's nomadic period, upon the observation of the phases of the moon, it could not, according to this view, be a fixed day. When the Israelites settled in the land and became farmers, their new life would have made it desirable that the Sabbath should come at regular intervals, and the desired change would have been made all the more easily as they had abandoned the lunar religion. [Jewish Encyclopedia (1901-1906) - "Sabbath"]

More from Jewish scholarship, admitting that the commandment of Hebrew Scritpure does not fix the Sabbath to a specific day of the week, and that Sabbath could be observed on Sunday without loss of true religion...

"... the phraseology of the commandment does not fix the six days (the definite article is not prefixed to [Hebrew given]); the definite article before "seventh" implies merely that the day referred to is that following any group of six consecutive days; the phrase "the seventh day" is found also in the Pessah law (Deut. xvi. 8), where it is evident that no fixed day of the week is intended.... The only consideration to be weighed is the unity of Israel. If all or most Jews were to observe Sabbath on the so-called first day in the manner in which it should be observed, namely, by abstention from work, the difficulty would be met without loss to true religion." [Jewish Encyclopedia (1901-1906) - "Sabbath and Sunday"]

Thus, according to even Jewish scholarship obedience to God's moral commandment to "Remember the sabbath day, to keep it holy" could be met by keeping Sunday holy, as has been the constant practice of Christianity since the 1st century.

God bless,

Dave