I guess they just aren't ready. Give them time, based on behavior they appear to be close.
Hows the comb color? My mature BRs have large very bright red wattles and combs.
Are they squatting? Do they have red combs?
What are you feeding them? Layer feed?
Might just need some time.
My barred rocks were born in February and started laying around late September/Early October if I remember correctly.