These are three distinct questions worth addressing separately because they each touch something real.
On mental illness and vulnerability, yes, inmates with serious mental health conditions like schizophrenia are among the most vulnerable populations inside any correctional facility. When someone's grip on reality is unstable, their ability to recognize exploitation, set boundaries, or advocate for themselves is compromised. Predatory behavior toward vulnerable inmates exists in every facility, and people with visible mental health struggles are disproportionately targeted. The Prison Rape Elimination Act was designed in part to address this, and facilities are required to have protocols for identifying and protecting vulnerable populations, but the quality of that protection varies enormously from one facility to another.
On sexual activity between inmates, it happens and it is more common than most people on the outside realize or want to acknowledge. Same-sex relationships, relationships involving transgender inmates, and situational arrangements that would not happen outside those walls are all part of the social landscape inside. Some are consensual and genuinely meaningful to the people involved. Some are coercive. Some fall in complicated territory between those two poles. Male inmates maintaining committed outside relationships while also having a relationship inside is something many people who have done time have witnessed firsthand. It is a real double life that some people compartmentalize completely.
On marriage and family while incarcerated, inmates can legally marry with warden approval at facilities that permit it, and many maintain existing family structures through the entire sentence. Raising children from inside is limited to communication and connection rather than physical presence, but family bonds are maintained and in some cases strengthened through the consistency of contact.
If you are concerned about a specific person's safety due to mental illness, contacting the facility's mental health department or ombudsman is the most direct path to raising that concern through proper channels.