Following on from what user said up thread about the way you and they talk, which you dismissed as nothing. Maybe it isn't nothing...
I have thought further about your post, owl. I may be totally wrong-but just guessing. There may be a dynamic going on for which you might be unconscious, unintentional. Yet, it may still be there, and your parents react to it none-the-less. I do not want you to feel that I am blaming you, but if you could objectively consider the possibility of this dynamic, it may help lead to a change that you are looking for.
It reads that your parents do not like you. Ouch. Or you moved out 12 years ago, when your sister was 12. So your parents may have fallen into a habit of treating her as an only child. Or Attila may be right and your family role was that of scapegoat-now out of sight, out of mind.
"Part of the reason for wanting to visit them is so I can visit her and her baby - who I want to know me well. "
This kind of strikes a chord with me. In the nicest possible way, it may just be phrased oddly but then again it may hint at your possible attitude of self-importance. Being university educated, artsy and "whimsical" would not excuse this.
This is subtle in your posting, but the way they talk points to it; the point that they are working class points to it; that they live for their weekends is a little dig; that your unmarried sister and fiance and baby live in an outbuilding (rather than saying it is a cottage or housed on the property, for example) is also a bit of a dig (as well as implied adult child still at home).
The awkward silences on the phone may be a defense mechanism against more digs.
they only begrudgingly pick us up from the train station if we ask
I don't think they would know to pick you up if you didn't ask though; they can not read your mind (do you give them notice, or just call and say "we're here-could you come now"?). Just a different point of view.
Having the built in rule/boundary to tie in a visit with some other event is a "kill two birds with one stone" put down towards you. It diminishes you and I know that stings (my sister did this to me all the time). But why would they do that? Is it similar to the awkward silences on the phone-less contact is less chance of subtle digs from you?
Your expectation of parental involvement and support for life is a bit precious, especially since you have proven that you are independent. You may possibly revise that perspective when you have your own. Perhaps they viewed your moving away as a judgement towards them? So their behavior is a kind of a consequence of that (payback isn't quite the right word)?
If any of this may be true, then you could try to change the way you treat them and talk to them about it (that being your behavior, not theirs). I know it takes courage and honesty to consider your own behavior. Now, with your pregnancy, and rocking prenatal vitamins
, you may find you have a new clarity of thought to consider this perspective. To get your parents involved- it might take a Mea Culpa (whether sincere or not) to get their attention.
If I am way out in left field here, I apologize. I hope that you can emotionally disconnect from them, if necessary, to protect your own mental health from the recurring disappointments. With the birth of your child, you may experience a psychological changing of the guard so to speak that may come with an epiphany of "what were you thinking?" You won't need your parents. You will need/could use some help, sure, but it doesn't have to be from your parents.