Here the words "know" and "am persuaded" mean basically the same thing; Paul uses them to emphasize his certainty. AT: "I am certain because of my relationship with the Lord Jesus" (See: [[rc://en/ta/man/translate/figs-doublet]])
This could be translated as a new sentence. AT: "But if a person thinks something is unclean, then for that person it is unclean and he should stay away from it"
AT: "If you hurt your fellow believer's faith over the matter of food" Here the word "your" refers to the strong in faith and "brother" refers to the weak in faith.