No, I don't think anyone else can travel on your behalf. Before confirming the booking of the redeemed package, they ask for you identity card, so I don't think it's possible.
Yes, one can travel from your redeemed credit. Tripoto says, you worked hard to earn credits so you could choose who will travel on your credits. But for more details you should contact Tripoto team and whoever is traveling on behalf of you ask him/her to carry vaild ID proofs
No. Most of the trip from Tripoto are on twin sharing basis. So you will get a discount on your share and you can bring along another company on his/her expenses.
No. it is strictly mentioned in the T& C. No other person can travel on your behalf. But yes the other person can accompine you, as the trips are on twin sharing basis.