Save the Gnosis ending for last; tackling it earlier messes up your save file, pushing you towards a not-so-great ending.
Make sure the other gods learn to think beyond themselves.

Amar : In general, get Amar to think beyond just partying and to think about others, even if Amar is scared. Encourage them to chat with Lutra when hunger strikes in the Kelp Forest. Amar should play with the twins at the Coral Reef.
Althea : Encourage her to consider others in her research. Give her a hand in rescuing the fish from the breach with Gnosis’s help. But don’t hand over any more pages to Gnosis till the last ending.
Lutra : Tell them to save food for later, even if it angers them. Get Amar to have a heart-to-heart about saving for others whenever you can.
The Twins : Respect their space. Get them to play with Amar BEFORE sending them to Lutra. Have Amar teach them some respectful play before sending them there. Fix the crystal with Althea’s help, but gently encourage them not to hold onto the crystal.
Get the Twins to help in Althea's lab. Althea will then be happier to help with the Crystal.

Hold off on crafting the crown till your very last dialogue with Elil. Create both the crown and the new world in one go to keep your save file intact. Basically this will ensure that your game is saved just before the very last conversation of the game (with Elil). After playing your first ending, when you reload, it will place you back to before you give out the crown.
Do not exit the dialogue after creating the crown. This will create a new save file, and in future saves you'll no longer be able to get the Gnosis ending.

To get the different endings, do the below steps and reload the final save file after each ending. You can do this in any order except for the Gnosis ending. This must be the last one as it will create a new save in which not enough pages are available for the crown

The endings and whom to give the crown for which

Powers for All Ending + Divine Harmony : Either skip the crown or give it to the Twins.
Rainforest Reserve Ending : Pass the crown to Amar.
Solar Punk Star System Ending : Crown Althea.
The Collective Ending : Hand the crown over to Lutra.

Reload one last time, but instead of heading to Elil, go to Gnosis and hand over all the pages. Now, go back to Elil, create the world, and boom! You’ll unlock the Panopticon ending and Theomachy achievement.

If you need help with specific dialogue options, this guide is good: https://sonicnancyfan.wordpress.com/

Tip: If you make a mistake along the way, remember to reload the checkpoint before exiting a dialogue. Every time you exit a dialogue it creates a new save file.