Is Zakah(obligatory charity) due on the Zakah money received by a poor person, and reached a Nissab( minimum amount liable for Zakah), and a whole lunar year had lapsed over having it in his possession?

Yes, the poor who possessed a Nissab for a whole lunar year is obliged to pay the Zakah due on that money even if it was given to him as a Zakah money in the first place.

What is the ruling on using bank cards such as Visa and MasterCard?

All perfect praise be to Allah, The Lord of The Worlds, and may His Peace and Blessings be upon our Prophet Muhammad and upo all of his family and comapnions.

It is permissible to use such cards in accordance with the following conditions : 1- The issuing body does not stipulate collecting interest upon late payments. 2- The merchant does not increase the price of the goods due to an increase in the commission collected from him by the card issuer.3- The purchased item(s) should not be gold , silver or currency in case the card is not covered. And Allah Knows Best.

Is it permissible for a person who broke fasting in Ramadhaan because of being sick to pay a ransom?

If there is hope for him/her to be cured, then he would be required to make up for the missed fasting days when he/she recovers, and no ransom is due on him/her. If his/her disease is incurable, then he/she would be required to pay a ransom for each missed fasting day, which is (600) grams of wheat, or rice.

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.