Nobody is sexually assaulted or objectified. The closest that happens is one shibito woman cornering another woman who is scared and pressing their faces together side by side, this is not used for assault and is instead used for a shared memory.
Miyako's guide dog dies off screen, but its body is shown in a relatively early cutscene while she cries over it. The dog does not have any blood or gore.
There are women that drown themselves or get harmed, but it is not for spectacle and there is not more attention brought to them than the men. Gender does not have to do with how much someone is harmed in Siren.
There is a cutscene of Miyako's older sister wanting to marry their adopted brother from what I remember. It is super brief and is not graphically shown at all. It is mentioned when Miyako is insulted by a taller woman that looks like her. (Please correct if I'm wrong, memory is foggy on this one)
Not a specific character, but there is a small moving mass of gore that is stepped on by Shiro in a cutscene. It is quick, and is similar to how an insect would be stepped on. The cutscene takes place after he finds a secret area underground and can be skipped with the Start or Select button (not sure which)
Kind of. After a cutscene of a shibito brain woman shows another woman a memory, that woman becomes a shibito and is acting as a sort of vessel for the shibito brained woman. This could be considered to be caused by means another than possession though.
It could be considered self harm in Naoko's post 2nd level cutscene where she slowly drowns herself. This is after the level in the school, and she is still alive for most or all of the cutscene while drowning herself.
After Akira's 2nd level's 2nd mission is completed, he successfully shoots himself. If you are playing the US version, this is not shown but the gunshot is still heard. After Naoko's 2nd level in the school, she successfully drowns herself, when Shiro and Kei meet in the shibito nest, Shiro holds a gun to his head and is implied to kill himself off screen, but he instead shoots Kei (also off screen) and after 'Kei's' last level where you have to take down two shibito women, he sacrifices himself and jumps down a large pit-like area. His body is not shown. These cutscenes can be skipped by using the start or select button, not sure which.
Tomoko feels rejected by her parents when she shows up at the church to meet them, unaware that she herself has become a shibito, which is why her parents react with fear. Tomoko sadly walks away, but is later reunited with her parents after they become shibitos too.
You could argue that Reiko (parental figure) "abandons" Harumi by sacrificing herself.
Shibito appear to cry blood. The Shibito "brains" (the "elite" Shibito. Killing it will kill lesser shibito in the area) usually lack eyes, instead having tentacles or other strange growths.
SPOILERS-
There is a scene between Kei and Shiro in the clinic level where Shiro is seen torturing two shibito women and there is an archive item describing what he did to torture them. The writing is not very graphic but the cutscene can be considered graphic. In another Shiro level, there is a corpse that seems to be starved in a basement, and it is required to look at to get an important item. Also, the last Kei level shows him driving a stake into one of the shibito women and she struggles the entire time, still alive.
A character's backstory involves the death of her child.
Many of the playable characters are teens or children, and are constantly in danger of a terrible fate.
At least two child characters die in the story. They can all die if injured enough, but that's a gameplay thing and not canon.
Akira shoots himself, thinking that'll stop him from becoming a shibito (it doesn't).
Shiro appears to shoot himself near the end, but it's heavily implied later that, instead of shooting himself, he actually shot his twin brother to steal his identity.
The shibito appear to cry blood. It's implied that the red water they bathe in might be blood (please correct me if I'm wrong!). Of course, being a horror game, this is expected.