They won't develop any sexuality other than what they were born with. If one or the other is homosexual they might be sexual or they may have no interest at all. They may have the desire to procreate. As for morals your question depends a lot on the character of the two people involved. Assuming they are levelheaded individuals, they will develop a moral and ethics code, because I believe that is innate. I do believe they would develop some kind of religion, because I think that comes from within.
I've thought of this same scenario myself. My scenario was several very small children, who don't even talk yet on a deserted island. Assuming they survive I believe they would invent the same things that man has invented. This includes a language, morals, ethics, fire, the wheel, mathematics. However, because man has evolved and we are now genetically stamped for these things, I think they would discover them faster than man previously did.