Hope you're enjoying the game! We'll try to drop hints if you get stumped. 
A Haunting You'll Never Forget, in This Point & Click Retro Horror Nightmare · By
Hello! You need to extinguish the 4th one before accessing the trapdoor or the other endings. I'll write a little hint to each candle as I don't know in what candle you are stuck.
Grandma: You need to Blind her...
Hanged: Once you turn off his candle you have to take him to 2 specific squares on the map...
Caged: You need a Music Box, You have to do Grandma's candle first.
Doll: You have to find the key in the hole and then open a locked door.
Thank you for your support and I'm sorry for the late answer. Hope you enjoy it!
Thank you, I'm really glad you enjoyed it! If you need one of the top candles, they are from the new prequel story, you need to beat the nightmare to have it. Once you have that ending, check the blood hole in the main game, and after you do that, try to do the a new life ending one more time, you'll know what to do. :)
If I remember correctly, you have to clear the game one more time as if you were doing the Baby ending, only this time, you'll pick up something in the lady's room before blowing up and lighting the last candle.
Here is a guide that someone from the Steam forums did in case that I misremembered: https://steamcommunity.com/sharedfiles/filedetails/?id=2258697371
Thank you for playing!
hmmm maybe i'be glitched it somehow, I go into the room when 4 are unlit and nothing is there, so I go and light all four candles to be black I go back in and there's nothing, in and out, still nothing, unlight her candle, leave and come back in, nothing still, so I relight her candle and I just get the baby ending?
In your ending screen there should be only one candle turned off, if there are more than one turned off then the letter won't spawn. If you do have all the endings, for some reason the game has glitched or something, because I tried to do the same thing you're telling me you did but I can't replicate the bug :(. I'm really sorry that this happened to you, if you have all the candles except for the last one I would recommend that you do a new run for the Salazar House story, and try to get the baby ending and see if the letter spawns. Please keep me posted, you can send me a twitter message https://twitter.com/Maldo19 and I'll get to you faster to see what's going on.