Need help with a rigid like skirt rig/skin

[alexandre.jaoui]

hello everyone i'm pretty new when it comes  to rig and skin  and i find myself in an issue that don't know how to fix.
long story short i have to rig a  rigid like skirt made of petal kind object  as seen in pic 1

i'm pretty happy with  all of my skin except for one part  the middle petal object( the blue one)  cause i want it  to follow both legs when they goes up  automaticly but i manage to make it follow only the left one see pic 2

and i try all of  th tings i know to make it follow  both see pic 3

i hope it's clear enought, thank you in advance
Alexandre