What is the ruling on the existence of cattles' marketplace of (Sheeps, cows and chickens ) inside a graveyard?

Graves must be respected, and it is not permissible to sit on them or show any disrespect. Establishing a marketplace within a cemetery is undoubtedly a form of disrespect to the deceased and is not permissible. Such actions should not be tolerated. And Allah Knows Best.

Should one fulfill his vow of donating an animal to the poor and needy with one sheep although he had repeated the vow several times?

Each vow has to be fulfilled, and repeating the words of the same vow for confirmation renders its fulfillment obligatory as one vow. As for multiple vows, they have to be fulfilled as well.

Is it permissible for the person who wants to travel from the United Arab Emirates to Jordan during the daytime in Ramadan to break his fast before leaving his country; knowing that he had embarked on journey half an hour after dawn?

Praise be to Allah the Lord of the Worlds.

The person who made the intention to embark on journey after dawn must observe fast for that day, because it became an obligation on him before engaging on journey. However, if he experienced unbearable hardship while on travel, then he is permitted to break his fast, but he must make up for the missed day. And Allah The Almighty Knows Best.

What should one who forgot to offer the second Sajda during congregational prayer, and remembered it before the end of the prayer do?

All perfect praise be to Allah, The Lord of The Worlds.                                                                                                                                                          Whoever forgets a pillar of prayer while in congregation must follow the lead of the Imam, and after the latter offers Tasleem, he should offer one Rakah, then perform Sujood As-Sahw (prostration of forgetfulness). And Allah Knows Best.