Seems like you don't want to use the "Something Else" option in the installer, but I recommend you do.
I recommend using gparted to build your partitioning scheme the way you want it, and after that use the ubuntu installer option "something else" and appoint those partitions you created for specific mount points (/, /home, /boot, etc.; also: swap)
see this question
The only difficulty here is that you'll need to make your own plan for the partitioning.
If you're using MBR/legacy mode, and both win7 and win8 need a "system-reserved" partition for booting, and if both windows's C: partitions must be primary, you have a problem. I don't know if grub's bootloader will be able to find a /boot partition on a lvm.
If win7 and win8 can both have their C: partition be logical, install them like that first:
- system-reserved partitions for win7 and win8: primary
- C: partitions for win7 and win8: logical
- /boot: primary
- /, /home, swap, etc.: logical
otherwise it won't work with MBR/legacy mode due to the limit of 4 (primary) partitions