Malboros attack with status changes, so you need to junction things like sleep, confuse, blind etc to status defence. If you have the 'Ribbon' item (I got it through the Chocobo world with the PC version), teach a GF that ability and select the command to the character, causing that character to not be affected by any status changes.

I can't remember much about the Ruby Dragons, sorry, but Shiva should be a good GF to use. I'm not sure, but I think 'breath' also creates status changes. If so, the same tactic for the malboro fight will help there too.

Hope that helps,
Jade.