I agree with Dammin, you can only do what you can do. You are doing a fantastic job, don't ever think you aren't doing enough or haven't tried enough. If you are happy for them to be bottle fed go for it and breastfeed when you can. When you get them home, just transition them back to full breastfeeding. For what it is worth, I have never seen nipple confusion in this situation, so don't let that worry you.