I'm a Jewish (Conservative movement) clergy wife. The others are right, it may be different if this family is very strictly orthodox, but here is my experience.
Your black pants are perfect. Even if this crowd wouldn't wear pants themselves, they wouldn't consider it disrespectful for someone else, especially a non-Jewish guest, to do so -- as opposed to something inappropriate like a tube top or sequins. Besides, people are very understanding about the foolishness of going out and buying a maternity dress just to wear to one funeral! You don't need to be dressed entirely in black or even necessarily in very quiet colors; anything dignified will do. Like anything you could wear to a courtroom.
You don't need a hat, but your husband will probably be asked to wear a kippah. If so, they will be provided. (If it's graveside, he can just wear his hat.)
I've never even heard of the superstition about it being bad luck for a pregnant woman to attend a funeral, and I wouldn't give that another thought. Even if this group believes that, you won't be offending them, you just might have to endure some repeated, tiresome comments. As a visibly pregnant woman, you are no doubt already used to that! (Miss Manners says learning to answer the same silly question over and over is excellent preparation for parenthood.)
Around here, most Jewish funerals are at the Jewish funeral home. A few are at the synagogue; a few are graveside only. If the funeral isn't graveside only, you don't have to go to the graveside or to the house afterward -- usually just the family and close friends do that.