My friend A's baby also has this problem and my friend B recommended this book for her:
On Becoming Baby Wise: Giving Your Infant the Gift of Nighttime Sleep
I personally haven't read the book. just post here in case u mums are interested.
For my baby, my husband uses a v. strict approach. let him go to sleep by himself. we play the classic music, dim the light...... most of the time, we will sleep after he is already sleeping. but sometimes, we are so tired that we go to sleep together w/ the baby. If the baby keeps talking, we simply ignore him. My husband said "let him feel bored. then he will sleep."
I don't know if this work on your babies too but i guess dim light and classic music may be useful.