Install Linux and PCBSD as you normally would. From there you make sure to install their bootloader to their partition, NOT to the MBR. Then after you have all 3 OS's installed you go back to Win7, add entries for Linux and PCBSD and test out the settings. EasyBCD wont configure or find anything. You tell it where you have that specific OS installed and you select the type of boot loader it uses. So you would select GRUB or GRUB2 and then select your partition for Mepis. You would then select the PCBSD section and point that to where you installed Isotope. You do all of it. From there EasyBCD just sets up the BCD to add those entries and when selected, they boot said boot loader.
So when you select GRUB or GRUB2 for Mepis, it will start the GRUB or GRUB2 bootloader and you will see that after making your Mepis selection. Same will go for Isotope. There is no perfect way to have the BCD just automatically boot into those OS's. So instead it just fires up their boot loaders.