In the name of Allah, Most Gracious, Most Merciful
Assalaamu `alaykum waRahmatullahi Wabarakatuh
There is no need to have a witness for talaq to take place. If a wife is given three talaqs, then it is not permissible to re-marry her until halala takes place. The procedure of halala is that after the wife completes her iddat of talaq, she will have to marry another man and consummate the marriage. Thereafter, the 2nd husband will give her talaq and she will complete the iddat of this talaq. After the expiry of her iddat, she may re-marry the first husband if they desire to do so.
And Allah knows best
Wassalam
Mufti Ebrahim Desai (F2)
Darul Iftaa, Madrassah In'aamiyyah
