I think my best friend is being haunted. How to know for sure and what to do?

I know this sounds crazy but my childhood friend is definitely being haunted. She lives in a rented house with her partner and her 2 kids, the eldest one from a previous relationship. When she was 20 she was with a guy for over 2 years and he died from an accident on a horse, he was a jockey. About a year after that she met her current partner and she got pregnant pretty quickly but over all they have a great relationship. Their daughter is now nearly 2. Last year after the baby's first birthday party someone had bought the baby a helium balloon. It was in the sitting room in the corner. One day both parents were in the sitting room and the baby was upstairs in the cot sleeping, all of a sudden really slowly the balloon started moving. It moved very slowly across the room while always touching the roof and always touching the wall. It proceeded to make its way out of the sitting room into the hall and up the stairs with my friend aand her partner following it. It then went into the bathroom at the top of the stairs around the four walls again then stopped in the corner for about 2 minutes, then moved again out of the bathroom and into the room where the baby was sleeping and stopped right over the cot and didn't move anymore. My friend and her partner were both shocked but after a few days thought no more of it. About a week later my friend awoke in the middle of the night to find her eldest daughter of 6 downstairs talking nonsense in the sitting room in the dark which the child is terrified of on her own. She went down to get her daughter and her daughter said she was talking to a man who was sitting in the armchair with his legs over the side of it but she didn't recognise the man. My friend was really scared coz obviously she couldn't see anything herself. She didn't want her daughter to be scared so she told her you are only dreaming but her daughter got really angry and said I'm not dreaming mammy I seen him. So the next morning my frind said to her daughter, were u having bad dreams last night and her daughter replied with, Mammy I told you I wasn't dreaming sure I was talking to him and I seen him. Anyway this was all months ago and nothing has happened since until last night the eldest daughter came into her mammy crying because she heard noises in her bedroom, I went with my friend today to collect her daughter from school and she told me that the noises sounded like her squeeky pink shoes and she was afraid, but the thing is my friend was up half the night before dat coz she heard noises too, not the same ones as her daughter but she said it was as if the house was moving or something. My whole point of writing this is because my friend has been suffering terrible with depression for the last 6 to 8 months, she's beautiful slim tanned girl but she hates to even look at herself. I called up to see her today and she was crying as soon as I went in. Her and her boyfriend are not getting on because of her depression coz she's always sad or being contrary. She's going to the doc to see if they can help. She's the most kind hearted person anyone could meet. I asked her today did she think that whatever or whoever is in her house is causing this because I have read somewhere before that ghosts latch on to people especially people with depression and can drain the life from them making them severly depressed. She said that when her and her partner are not in the house if they just go for a walk or whatever they always get on really really well while they're not in the house but as soon as they get home they're arguing again. the other day her boyfriend screamed at her saying " its this ******* house". If anyone has any experience with this kind of thing can u please write back because I cant bear to see her this way anymore. I kind of feel like it's her boyfriend that died that's haunting her. Please no smart answers I undersstand that this is all hard to believe but it is what is happening