I hate to rain on the parade - but yout question cannot be reasonably answered as
1) We know nothing of the AI fleet size and composition
2) what you want to do with them
What I mean by this is that the offensive fleet could be split in two and dominate both AI, or alternative a single AI could hammer both of your fleets if they were combined.
There is also the issue of not knowing how you are going to apply the offensive fleet - to kill the AI fleet(s), capture planets or kill infrastructure.
Sins is very hard to apply specific formulas to as each game is different - but a balanced fleet (which they seem to be) is a definate plus.
Sorry not to be more helpful, but there are too many unknowns, and even then, everything would be a best guess.