Their is the possessive form of they; there refers to place; and they're is the contraction of they are.
त्यो अवस्थामा सर्वोच्चको वरिष्ठतम् न्यायाधीश उनै रहन्छन् र त्यही आधारमा उनी न्यायपरिषद्मा रहने भए ।