Should the Zakah(obligatory charity) giver tell the poor recipient that this is the Zakah of his money?

No, he shouldn`t. But, the Zakah giver should make an intention in his heart that it is the Zakah of his money when he gives it to the poor.

Am I permitted to perform more than one prayer within single ablution?

You are permitted to pray as many as you could within one ablution and to recite Quran so long as your ablution isn't nullified.

Is everyone obligated to follow the fatwas of his country, and if we adopt the fatwas of scholars of other countries, is it considered a sin?

: It is permissible for one who do not specialize in Shari `ah sciences to apply the opinions of renowned scholars whom he trusts ,whether they be from his own country or not ,but if the scholars don`t arrive at a consensus concerning a certain matter then he must consult someone who is more knowledgeable than himself .It is preferable that you(the inquirer) specify the case of your interest ,so that we could give you a more specific answer since some scholars deliver fatwas based on atypical opinions which should not be applied no matter what .And Allah ,The Exalted, knows best.

Is it permissible to pay the expiation of an oath to a charitable party as it feeds the poor and needy such as Tkiyet Um Ali?

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

There is no harm on authorizing someone to handle the expiation of another to the poor and needy, since Shafiee's jurists stated that authorizing someone for the purpose of distributing Zakah, expiation and vow is permissible as stated in [Mughni Al-Muhtajj, vol.3 pp.237]. At last, the intention of the person who intends to authorize someone else suffices in this regard. And Allah Knows Best.