Some families are closer than others, that's just life! So yes, I expect that at times, some royals are chummier in front of the cameras than they are in real life. However, I expect others really do like each other, and this changes!
There are some royals who are known to not be too fond of one another, and so don't spend much time together away from the press. (I think I remember hearing that Stephanie and Caroline of Monaco were like that, at least for a time)
Everybody has those little "issues" when they are annoyed with their family- if you have a spouse or significant other, haven't there been times that you are mad at them? The royals go through that too (there are other threads on some of those types of topics- cheating, marital troubles, etc)- but they have to pretend that everything's okay. If people don't, then you get what happened when Charles and Diana and Andrew and Fergie split- a big media mess that drags the monarchy through the mud. (If you do act nicely when things are going that poorly you get what happened when Joachim and Alexandra split) Even the most loving royal couples have had their spats, and they deal with it.
I'm not sure that I believe that any of the current royals (at least of the crown princes and that generation) married to "continue the royal line". If they wanted to, there were generally probably more "suitable" women- women without "pasts" or "family issues"- whatever.
Is there a major pressure for them to have babies? Yes, in the media, because babies are cute, and well, "first comes love, then comes marriage, then comes the baby in the baby carriage". (But Camilla pregnant?
) Crown Princess Masako of Japan has famously had stress issues in the past years, and common speculation is that much of that has come because of the pressure on her to have a son. Only recently has she returned to the public spotlight.
Sophie, Countess of Wessex put most of the pressure on herself to have another baby. After reported warnings from doctors about the risks of her having another baby after all the troubles she had both when Lady Louise was born and before, she still wanted another baby. Finally, it seems she is getting her wish.
The end of this very long post.