I always quick reply and not quote
About saving Solaire.
Step 1: Join Spiderboobs Covenant
Step 2: Get 30 humanity
Step 3: Die
Step 4: Die again ASAP
Step 5: Hahaha, you need to get 30 more humanity.
Step 6: Give up 30 humanity to Spiderboobs
Step 7: Open gate
Step 8: DO NOT PASS THE GATE.
Step 9: From as far away as possible, while still not crossing over into the new area, snipe as many maggots with your bow as you can
Step 10: STILL DO NOT CROSS
Step 11: If you're sure everyone is dead, play the level like you didn't open the gate.
Step 12: When you arrive from the other side of the gate, Solaire is still alive!
Step 13: Fistbump your Sunbro.
Edit: It's very picky about how far you advance. If you cross into the area no matter what you do, Solaire dies.