My wife and I have started to share some of our fantasies and stories....my wife always seems more reluctant to share than me but eventually warms up to it? Is this normal?
Also, she has finally admitted that she fantasizes about other men (faceless) take her from behind in her favourite position..... is it normal for women to not want to share that they get aroused thinking of others?
A few random thoughts. "Normal" can also refer to a bell-shaped curve. For something to be within a normal distribution range means it can be pretty far from either the mean or the median and quite unusual. Some things are just more common than others. You are individuals, focus on what you both want or would find interesting to try. Don't worry about what others may or may not want to do or how common it is the things the two of you both want to do.
The Sex Therapist who helped my wife and me save our marriage had us take a Yes/No/Maybe list separately and then share them after we had filled them out. That is a good way to initiate sharing of sexual desires among a couple and can even includes some fantasy sharing.
Some sexual fantasies are best left to the imagination. Role playing can expand the range of sexual acts that can be safely dabbled in. However, all sex should be consensual and should no emotionally harm the marriage.
Someone commented about how you can't have a 12" penis in real life, even if it was your fantasy. Well in a role playing fantasy, you can have either a 12" penis sleeve or strap-on dildo and if your imagination is strong enough that might allow a person to live enough of their fantasy.
There is an interesting TED talk on monogamish about how one can role play a 3-some and yet maintain fidelity if it is important to you (and for most as she points out earlier in the talk open relationships don't often work out). I don't hold much of what she says, but the part at about the 10 minute part does show some ways that a couple who wants monogamy can add non-monogamy role playing to their sex life.
Jessica O'Reily Vancouver TED talk on Monogamish
I would say that sharing sexual fantasies takes a lot of courage and so it is not that common. When my wife and I did our Yes/No/Maybe list suggested by the Sex therapist, my wife reacted quite negatively to some of my maybe's. Which required a little extra discussion by the Sex Therapist.
A comment that has stuck with me is "Q: If a husband can't tell his wife his deepest and darkest sexual fantasy to, who can he? A: A prostitute who will respectfully listen, not judge him, and figure out how much she will charge him for it." The point is that you should be able to share your deepest darkest secrets with your spouse. You the two of you should be able to be vulnerable with each other and share taboo thoughts, with fear of being put down or shamed.
Good luck on you and your wife's journey of exploration, but be careful.