Family Visit Dilemma

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About 4 weeks ago, my husband and I made plans to drive down to San Francisco the beginning of Sept. (from Vancouver) for a long overdue visit with my sister and sister-in-law and planned to spend just a few nights with each of them. My other sister kindly offered to fly over from Calgary to house-sit my cats while we are away. In the interim, I received the news that my unwed niece (in SF and age 28) is 6 mos pregnant and has broken up with the father. My sister and her husband kept this from the family all this time because they were devastated and had some damage control to do before announcing. Things have settled a little, my niece will have her baby in Nov. but the situation is still quite fragile. This, coupled with a recent strained relationship between my sister-in-law and her boyfriend is going to make our trip very uncomfortable and we just don't feel like going! The dilemma of course is that if we cancel, we disappoint too many people and then we've got to deal with our guilt. However, to make that huge drive down there and the expense of hotels, etc. would end up being one costly and heavy-duty (emotionally) trip. We want to be supportive, but figure the timing of all these latest events is simply bad and would rather go when everybody is up and happy. We sent subtle hints in emails to this effect, but of course they said they were glad we were continuing with our trip but we get the feeling they are just being polite. We do see each other every couple of years, so it's not as though we couldn't wait for a better time. Any advice out there would be most welcome.