I think that your advice to your friend is very sound (see your second-to-the-last paragraph). Until she talks to him, there is no way to truly speculate why he is acting the way he is. In my own experience (my husband's actions during my own pregnancy and then raising our son), men don't fully understand what it is like to be pregnant, and I had to sit down multiple times with my sweetie and explain, time and again, how tired I was, how I felt sick, how my hormones were hijacking me and taking me for a ride, etc., but it took a while for it to set it. What also helped (along with these talks) was a couple easy-to-read pregnancy books/magazines. They have them at the doctor's office, "How your baby is growing" kind of thing, with photos and pictures and week-by-week updates on how your baby is developing and how it affects the mother. For a man who likes to be in control, this helped a lot, because he then felt like he knew what was going on.
Her fiancé could be acting out of stress. He could be trying to plan nice vacations for her because he is trying to be supportive and do something nice for her. He could be not ready (more likely he just THINKS he's not ready). Whatever is the case, they do need to talk, and yes, she should keep her hormones in mind. Hormones can take an innocent comment of his that she normally would understand and blow it up into something horrible and mean and insensitive. She also needs to keep in mind that he is a man, and thus has no way of fully comprehending what she is going through unless she explains it to him, over and over again. Think of it as teaching him about a different culture (which is actually exactly what you're doing).
A good tip for her: if he says something that seems insensitive, BEFORE SHE REACTS TO IT, have her say this: "Okay, this is what you said, and this is what I heard and how I understood it. Is that what you meant?" He should do the same. It's the whole "Mars vs. Venus" translation trick. Half the time, how one person understands a comment and what the other person actually meant are two completely different things.
You would be amazed how well this works. My husband and I understand each other much better now, because we learned to do this when I was pregnant, and it saved us from many a fight.
Obviously things need to be done around the house, but when you are pregnant there is only so much you can get done, and you don't need someone constantly pointing out what work you need to do. Repeated explanations and her standing her ground (without blowing up in a hormonal freak-out; a lesson hard-learned by me) are probably what is needed. He is a man going from the single life with no responsibility but to himself, to suddenly becoming a married man and the father of not just a new baby, but a seven-year-old who is probably going through some adjustment to the new man in their life. This is a HUGE change. Expect some crazy moods from him as he adjusts to his new life.
My brother was in a similar position a few years ago. Bachelor, college, independent, and within four months he met a girl, asked her to marry him, two weeks later found out they were expecting, two months later they were married, and then he had a mortgage, a wife, a brand new baby, in-laws who weren't crazy about him, and all of his plans for the next few years faded into the distance. He handled it okay, until two years later. They survived, but it was a rough couple of months, and you know what? All it was, was him feeling the effects of his life changing so dramatically, and feeling the weight of the responsibility of being the man-of-the-house, providing and protecting and caring and loving a wife and his son (with a second baby on the way). She reassured him that if he wanted to do some of the things he had planned on doing when he was single– like traveling, having one night a week to hang out with his friends– she was okay with it. So he went on a road trip to Colorado for a week (and actually came home a day early because he missed her so much), once a week he has an evening all to himself and his friends, and he loves her and his kids even more and I've never seen him happier.
Okay, this response ended up a lot longer that I had planned. Sorry. What it all boils down to is, they should talk. She needs to be patient, he needs to be understanding, and it might take a little for him to wrap his head around the huge change he's going through. It does not sound like he wants out or is reconsidering their relationship. He, as you said, did not have the best parental role-models, and so is struggling with what it means to be a husband and a father. Despite this he is there, working hard, planning vacations for her to relax (so he is trying, even if he is forgetting to make sure the vacations work with her schedule and her kid's school). Sometimes he may be insensitive (guys react to anything that isn't happiness the same way: they get angry, or over-controlling), but he is trying. It happens to the best of us.
On the flip side: if he does not change, after their talks and with premarital counseling (a must for anyone getting married; helps iron out a lot of potential problems), then she will need to make a very hard decision. While my brother's story worked out, I have a friend who married a guy who also acted in much the same manner as your friend's fiancé, and they have now been married for three years, and he has not worked a single day. They are expecting their second child, and through it all she has had to be the bread-winner, as well as come home and take care of the house. Not the kind of man I thought she should marry, but she did.
Talk. Communicate. Work it out. Have premarital counseling. I really, really pray things get better, and that your assessment of the situation is correct.
Hope everything works out, and I will pray for your friend!
God bless!
M.