I eould say GP mad... no reason why not br feeding would make any difference. I also used the toddler taming book. and it sorted out sleeping problems immediatly... almost, with a bit of work from me, and a few sleepless nights. IN the long run, it was well well worth it.
I still br feed DD ( 16months) before bed, and first hting in morning, also in the day at times when she wants/needs it. PLus now if she wakes in the night, I do feed her, happily, knowing that she will go back to sleep and that it won't be the same every night anymore.
The book is called Toddler Taming by Dr Christopher Green and hasa sections on everyhitng you can think of, including a really good method on sleep training - since that is what you will have to do now at 18months. UNless you are happy to stick it out ntil your DC sleep through by themselves.
Its a kind of Controlled crying, but not as harsh, much easier to do, and kinder on them. Its very gradual, and DD was fine and has slept better in the day time as a result. It changed our lives, it really did.