Can I accept two answers on a question? Is the points / reputation given to both of the user who answer (15 points / reputation for each accepted answer on a question)?
You cannot accept more than one answer at a time. That is, a question can have at most one accepted answer.
Assuming the accepted answer is by someone other than yourself, its author will get 15 reputation, and you get 2 reputation for acccepting an answer. (If you accept your own answer, you don't get any reputation from this.)
If you change your mind about which answer to accept, you can unaccept it (by clicking the green check mark). This allows you to accept a different answer. You can also unaccept an answer if you realize it does not really solve the problem as you had thought--that is, unaccepting an answer you've accepted doesn't require that you then immediately accept another answer.
If you unaccept an answer, you can reaccept it later (perhaps once it's been edited...).
Unaccepting an answer reverses reputation given for accepting it. That is, if you unaccept an answer written by someone other than you, they lose the 15 reputation points associated with having the answer accepted, and you lose the 2 reputation points associated with having accepted an answer. If you unaccept your own answer, there is of course no reputation change.
If you've accepted an answer and another emerges as clearly better, you should probably unaccept the old answer and reaccept the new one. But you're under no obligation to do so, and in general it is a good idea to wait, not for too long, but for long enough before accepting an answer that you have good reason to believe you won't want to unaccept it later. On the other hand, if your question is answered quickly and the answer totally addresses and resolves the question, it's certainly OK to accept it without waiting for more answers.
If there are two answers of equal worth to you, I suggest accepting the one that you think may be of greater worth to others with situations similar to yours. If you cannot decide on that basis either, you should simply pick one arbitrarily.
In your particular situation, as you know, you have enough reputation to upvote answers. Since you have two answers that are worthy, you should of course upvote them both; this will lead to them both being recognized by others as valuable, and each upvote will give 10 reputation to the author of the answer. Therefore, you can give reputation to more than one answer's author, even though there can only be one accepted answer.
Some users only use Ask Ubuntu for a very short time, perhaps to get a single question answered. And that's a perfectly OK way to use the site. However, for users who use it longer, most find that getting 15 reputation happens pretty quickly. At that point, one can then go back to their old questions (that they had asked before they had the privilege to upvote answers) and upvote all worthy answers, including (but not just) the accepted answer. It is even quite reasonable to upvote answers before accepting any, since upvoting an answer just means you think it's good, not that you think it solves the problem for you or is the best answer.
Finally, for the benefit of users who have not yet gotten the ability to upvote answers: When you do, this is not limited just to answers to your own questions. Once you hit (or exceed) 15 reputation, you can upvote other questions, as well as answers to other questions. And you can cast votes here on meta as well (once your reputation from the main site is synced here, which happens relatively quickly).