What will it take for this to happen? Nerves of steel, for starters! Then it requires a very clear picture of your vision for your children. You want them to be self-sufficient and independent, resilient and confident. Keeping the bigger picture front and center, and acting on it, will allow your children to become responsible for themselves and grow up.
The idea of unconditional love has been misunderstood. It means loving someone because of who they are, and in spite of who they are. It does not mean accepting what you find unacceptable with a smile and hoping they'll get it one day. Temporarily giving up the 'relationship' will be necessary. Sit on your hands. Speak the truth. Put your desire for harmony to the side. Make and follow through with the tough decisions. (I know, I know. It's painful.) When they hit road blocks, you hit your own roadblocks, wanting to fix it for them. Fixing is not the same as guiding and teaching. Fixing will stunt their emotional growth.
You may think this is tough love. It feels like it, but don't confuse it with lack of caring. What it is is good parenting, effective parenting. It may feel just the opposite of love... but in truth, giving your kids what they need is the ultimate, highest form of love.