my hamsters are suddenly fighting

Question
I have one male sapphire hamster, just call him john. for a few weeks he was alone because the other hamsters died. so I bought him another sapphire hamster to keep him company.
at first, I planned to buy one female for company but then I changed my mind and bought a couple instead, just call them joni and nina.

I tried to bring joni and nina to meet john, my lone survivor hamster. And they got along quite quickly. soon they became friends and I put them together in the same cage. they slept together, played together just like any happy hamsters. Until suddenly one night after a few weeks or approximately one month and few weeks later, JONI and NINA got into a huge fight.

I dont know whats wrong or what they've gotten into, they just started fighting like a bunch of mad dogs and i swear there had never been ANY problem or whatsoever before. the 3 of them have always been so peaceful. I love animals especially hamsters so I've always paid extra attention to my hammies.

now the funny thing is, only joni and nina that gotten into a fight. john, on the other hand, had no problem at all! he still got along well with nina! and out of the blue, nina just hate joni. she will always turned into some kind of a monster whenever she's near joni. So she would cuddled and played together with JOHN, but NOT with JONI! now joni's always alone in the corner :((((
anyway, I decided to just separate joni alone for now, while john and nina are still in the same cage.

but im still depressed! what should i do now?? why are they suddenly fighting like this?? this is no ordinary fight. they fought like they are two different hamsters that just met each other!
I swear i feel like im watching some hamster drama here!
please help me pleaseee :((

Answer
Syrian sized Hamsters are naturally solitary animals and will fight when put together. Dwarf hamsters can live in same sex groups but are know to fight and kill each other when non litter stock is added and in male groups even when related at maturity. Once 1 starts to fight the others may follow suit.
The solitary hamster should be kept a part from the other 2 permanently.
you should not be putting male and females together unless you want to breed and to do this you must have multiple cages and know the background of the stock you wish to breed. Never breed litter mates or gentically related stock.
The female cannot be kept with the male when ready to give birth.