How do we determine who is right and who is wrong when everyone claims to take his stand from the Bible?

Answer:

"Sanctify them by Your truth. Your word is truth" (John 17:17).

"Therefore do not be unwise, but understand what the will of the Lord is" (Ephesians 5:17).

How do you know how long a meter is? Do you go up to ten people and ask them if this looks like a meter to them? And since you'll get different answers, do you conclude that it isn't possible to know how long a meter is?

Your second question shows that you accept that the Bible is the standard for guiding people's lives. You know it is a fixed standard. The fact that people give different opinions about what they think the Bible says or ought to say on a topic doesn't change the fact that the Bible is still the standard of measure. "All Scripture is given by inspiration of God, and is profitable for doctrine, for reproof, for correction, for instruction in righteousness, that the man of God may be complete, thoroughly equipped for every good work" (II Timothy 3:16-17). God, through the Bible, has told us what is right (doctrine), what is not right (reproof), how to get right (correction), and how to stay right (instruction in righteousness).

There are people who distort the truth. "Therefore, beloved, looking forward to these things, be diligent to be found by Him in peace, without spot and blameless; and consider that the longsuffering of our Lord is salvation -- as also our beloved brother Paul, according to the wisdom given to him, has written to you, as also in all his epistles, speaking in them of these things, in which are some things hard to understand, which untaught and unstable people twist to their own destruction, as they do also the rest of the Scriptures" (II Peter 3:14-16). However, the presence of distortion doesn't mean there is no truth. It means we have to compare what people claim to what the Bible actually says.

So, in regards to the time the Lord's Supper is taken, see: Should the Lord's Supper be only taken at night? for a discussion of the verses involved.

A child having an SS chromosome means the child will be shorter than average. That is what SS stands for: short stature. That is why abortion is wrong. People are killing children who do not meet their standards of acceptable living. Where would poor Zacchaeus be if his parents had such foolish doctors? "Now behold, there was a man named Zacchaeus who was a chief tax collector, and he was rich. And he sought to see who Jesus was, but could not because of the crowd, for he was of short stature" (Luke 19:2-3). Accept that a child born is the child God entrusted you with. I'm more impressed by a local couple who found out that their child had a problem that would not allow him to live more than a few years. After getting over their grief, the couple determined that while they had the child, they would make his life as happy as they could so he could enjoy his brief time on earth. When he finally did die, they thanked God for loaning them such a precious gift. Children are to be loved, not picked over like fruit at a supermarket.