Dear Kate,
As Lorraine has said, what a very kind jesture to want to find out more to help your sister through this difficult time.
My personal feeling would be to contact your local Early Pregnancy Unit. They have details of support which can be obtained for those having suffered a miscarriage. Even if your sister feels unable to face the world - and this can take some time (I took at least 4 weeks after my ectopic before feeling even remotely ready) - I'm sure you would be able to get pointers for yourself.
Although as her sister you are close enough to be able to give some very good support, I think you need to talk to your BIL. Even if he isn't coping well, he needs to be your sisters main supporter since it is very easy in these circumstances to mis-interpret non-support for non-caring. If you can make him see (in a nice a way as possible) there is a chance of loosing his wife if he doesn't grieve with her, it may also bring your sister out slightly if she understands his pain too (easier to be a supporter than be supported ones-self).
Also, is there anything you can do to perhaps commemorate your little neice/nephews being - one girl on here planted a tree in honour, another I know has a website
http://www.geocities.com/ourangel_baby/ where you can join her virtual candle. Maybe something you can gently discuss with your sister which suits her - best not to organise this yourself but together since it will help your sister to hopefully move to a different state of grief.
Your sisters little baby will never be forgotten and has a special place in your hearts and with the angels and I'm sure all of us would wish that they get a little sister or brother to watch over. Even those of us with major fertility problems eventually see (although this can take months) the advantage of having been pregnant - not all hope is lost. There must have been some reason unknown to us, why they did not make it.
I wish you all the best for you and your sister and hope that you can find the answers you need to turn the corner to a better place.
Lots of love
Fiona xxxx
Me:36 Dh:46, ttc 5+yrs, M/F (96% abnormal).
13 unsuccessful Txs From 2000 [4xClomid (NHS), 7xIUI(d)s & ICSI#1 (MFS), ICSI#2 (MFS) Oct 02 (ectopic)] Natural pg Jan 03 m/c 5.5wks
ICSI#3 (CARE) +ve boy (Xander) EDD 21/03/04 - so excited!!!!!!