TR: I can think of better ways of grieving for the loss of your FIL than his precious DIL spreading cigarette toxins through her body - not to speak of his unborn grand-child...
I read briefly about your PND, stepkids, and submarine man too, so I can imagine your situation may be harder than most, but to be honest, I'm not sure what you're doing is acceptable.... And I don't think you do either, or you wouldn't feel guilty about it / be worrying about 'getting caught' etc.
I've posted a few times about a book by a bloke called Carr - 'How to Stop Smoking' or something like that. Have you tried reading it ? Get it from the library if money is tight, or post here and someone will probably offer to sell you one they've used. It has a lot of useful information and suggestions.
Sparklymieow quit 4 days ago, stinkmamma quit last night (I think), and it might help you to continue to post here and discuss your feelings / concerns / how you're coping with the cravings etc.
Good luck.