Overgrooming, nicks, less heat cycle

(Photos attached below) Hello! This is about my 2 years old female cat, Peach. She is a healthy cats weighing between 4 to 5 kg (8.8 to 11 pounds) She overgrooms and nibbles hence there is missing patches of fur on her hands, thighs, base of tail and stomach to groin area. Due to nibbling, she has cuts all over these areas. She lives with her siblings, 2 female cats. All of them are not neutered yet. Peach also sometimes fights with her siblings, mostly with one of them. Also when one of her sisters would go upto her and smell her, she would attack her. Sometimes her sisters starts the fight. But they are not fighting all the time.These are always small fights, one of them runs away and it ends. She is not aggresive towards us. Also Peach goes into heat less times than the other 2 females. For example, if the other 2 goes into heat 1-2 times a month, Peach goes once in 2 months. They share one big litter tray since they were kittens. I have separated their food and water bowl few days ago, but still I see them eating/drinking from same bowl. They eat both dry and wet food. Dry food is available all the time for them. They are indoor cats. No ticks. They are vaccinated. All of them spray but mostly urinates around the house, like on sofa, behind doors, in a corner,etc. Their litter tray is kept clean. I guess they mark areas by sitting and urinating (which is larger amount of urine than spraying), which I clean with a floor cleaner to remove the smell. She chews and eats small amounts of plastic from carry bags and sometimes would vomit it out. Thank you dr 😺

Hello - there are some red flags regarding stress here; Peach is living in a multi-cat household and doesn't seem well settled in the social structure.  The cats are also sharing one litter tray.  In the wild, cats arent particularly social; they tend to spread out so that they occupy different territories for much of the time, and go for different toileting sites, even compete over them.   They are opposite to a dog in that they  dont have the highly evolved social structures;  conflict is often ignored until it is settled - or more commonly, not settled - with a fight.  The building tension can be a common cause of stress and overgrooming - especially in the presence of a slight allergy - and that isn't an easy one to solve.  Inappropriate urination / urinary problems can also occur for some cats at these times.  Obviously its a good idea to see your vet to rule out other causes of that rash, but the one radical move that would make life less stressful for your cat might turn out to be to rehome her somewhere with no cats, which sounds extremely dramatic but can make a huge difference.  However, less dramatically, there might be some ways to help the social aspect, including a litter tray per cat and a spare, spread out across the territory, for example.   Sarah Caney writes about stress in cats a lot on her website icatcare, and you will find some articles about stress and multicat household in our blog.