first game - being attacked by two neighbours. how do i stay alive?

I'm playing my first serious game, turn 90-ish, two neighbours declared war on me. We are roughly the same strengt. I have one military star base protecting one planet that is the closest to one enemy faction. I have basic weapons, 17 logistics size, and a few fully upgraded fleet (armor, shields lv 1)

 

I have another neighbour that is the most powerful, maybe they can help out?

 

How do i survive this?