Same here!!
You’re not doing anything wrong - some babies are more alert than others, some more sensitive, some have lower sleep needs etc. could they be either over or under tired? Usually babies this age can’t hack being awake for more than 1.5- 2 hrs max so if they go beyond this it may get hard for them to switch off as they’re over tired.
This is my baby sleep holy grail! https://possumssleepprogram.com
barely any, only sleeps with a contact nap x