Romans 14 is not about the Sabbath. It is about judging a weaker brother...
Rom 14:1 Him that is weak in the faith receive ye, but not to doubtful disputations.
Rom 14:19 Let us therefore follow after the things which make for peace, and things wherewith one may edify another.
Rom 14:20 For meat destroy not the work of God. All things indeed are pure; but it is evil for that man who eateth with offence.
Rom 14:21 It is good neither to eat flesh, nor to drink wine, nor any thing whereby thy brother stumbleth, or is offended, or is made weak.
And two subjects are dealt with, vegetarianism...
Rom 14:2 For one believeth that he may eat all things: another, who is weak, eateth herbs.
Rom 14:3 Let not him that eateth despise him that eateth not; and let not him which eateth not judge him that eateth: for God hath received him.
And fast days...
Rom 14:5 One man esteemeth one day above another: another esteemeth every day alike. Let every man be fully persuaded in his own mind.
Rom 14:6 He that regardeth the day, regardeth it unto the Lord; and he that regardeth not the day, to the Lord he doth not regard it. He that eateth, eateth to the Lord, for he giveth God thanks; and he that eateth not, to the Lord he eateth not, and giveth God thanks.
Notice...
Luk 18:11 The Pharisee stood and prayed thus with himself, God, I thank thee, that I am not as other men are, extortioners, unjust, adulterers, or even as this publican.
Luk 18:12 I fast twice in the week, I give tithes of all that I possess.
did they fast twice in a week? Yep. On particular days? Yep! From John Gill's Exposition of the Entire Bible...
I fast twice in the week,.... Not "on the sabbath", as the words may be literally rendered, and as they are in the Vulgate Latin and Ethiopic versions; for the sabbath was not a fasting, but a feasting day with the Jews; for they were obliged to eat three meals, or feasts, on a sabbath day, one in the morning, another at evening, and another at the time of the meat offering: even the poorest man in Israel, who was maintained by alms, was obliged to keep these three feasts (f). It was forbidden a man to fast, until the sixth hour, on a sabbath day; that is, till noon (g): wherefore, it is a great mistake in Justin (h) and Suetonius (i), that the sabbath was kept by the Jews as a fast. But the word is rightly rendered, "in the week"; the whole seven days, or week, were by the Jews commonly called the sabbath; hence, , "the first of the sabbath", and the second of the sabbath, and the third of the sabbath (k); that is, the first, second, and third days of the week.
Now the two days in the week on which they fasted were Monday and Thursday, the second and fifth days; on which days the law of Moses, and the book of Esther were read, by the order of Ezra (l); and fasts for the congregation were appointed on those days (m); and so a private person, or a single man, as in this instance, took upon him, or chose to fast on the same
: the reason of this is, by some, said to be, because Moses went up to Mount Sinai on a Thursday, and came down on a Monday (o). But though these men fasted so often, they took care not to hurt themselves; for they allowed themselves to eat in the night till break of day. It is asked (p),
First notice that they did not fast on the Sabbath. Secondly, they fasted on Monday and Thursday. Paul is addressing those who thought if one did not fast on Monday and Thursday they were somehow weaker and inferior to the those who did. He was addressing fasting on Monday and Thursday.
Romans 14 is not about the Sabbath at all.