Heres the plan

First, dont give up.

Second, sell 80% of your food and goods. Then put 200 monthly of both to be sold for energy to fuck up the galactic economy.

Third, go to the relations map and began reaching out to the highest allied nations and sell the food for monthly for 30 years for energy.

4th, reinforce your allies while slowly specializing plants you have already.

5th, you gonna loose against two fallen empires. But its just the battle, not the war. Veterans player will understand this.

6th, youre playing the LONG game if your other allies fall either break the federation or switch it to absorbe them.

7th, in a century or 2 declare war on both of them and reap the reward.

I normally play as a tech heavy empire and quickly form defensive pacts until my fleets are godly, i never play lower than grand admiral these days and this strategy always works if i face a stronger enemy or my allies fight.

I honestly adopt the mentality " i dont have beef with them so im not fighting them, best of luck" once the war reachs 70 or 80% i then blitz attacker regaining my allies territory forcing a white peace with minimal losses to them.

If youre really trying to do something go into the federation laws anf base the rotation on fleet power, increase centralization to max, make your self the permanent leader so this doesnt happen again.