You can resurrect Darleen, if you have the O-Nomitron.
See Two_jeff's buyable collections (he is here, in this site). Install them in your "collections" folder, in my documents/EA games/TS2/collections.
Bella and Skip have to be revived only, can't be resurrected.
Skip:
1) Simpe/tools/neighbourhoods/Pleasantview(tumbnail) - open.
2) Scroll down to Neibourhoods/memory in SimPe.
3) Scroll to Brandy, and delete the memory of Skip's death. Click on "commit".
4) Scroll to Dustin, and delete the memory of Skip's death. Click on "commit".
Files - Save.
5) tools/neighbourhoods/sim browser: Click on your keyboard S until you reach Skip Broke - there are two, the real Skip is user .....90. - open.
6) in the section "other", delete the check of "is a ghost". He is the smiling one.
7) Here you have a problem, because you will be stucked number of times (there is some bug in the SimPe), so be patient.
neighbourhoods/memory - click twice on the scroll column, and then quickly drag it to the half way down.
If you get stucked, "end now", and try again.
When you reach Skip - highlight his tumbnail, and delete the two tokens - "I am Dead". After each delete click on "commit".
Edit: Just now discoverred new trick - after two clicks on the scroll column, click on your keyboard S (for Skip), it will go to the all "S" in the game; the second or the 3rd is Skip - pay attention that he is user 90, and not user 19.
Save
Exit.
Use the Inge's teleporter, and teleport Skip. He is in "defaults". Brandy has to propose again engagement and marriage.
I just revived Skip, and changed his character too: I made all the family Knoledge sims, change all their aspirations to Knowledge, and gave him a Taurus zodiac sign (attracted to Aries - Brandi).
The same you have to do with Bella, she is easier to get (at the beginning of the memory table). Don't forget to delete Mortie and Cassie's memories of her abduction.