Cats keep fighting, advice needed please

[AChickenNamedDoris]

Hi, I'm seeking advice on behalf of my sister. She got two rescue cats about 6 weeks ago. Unfortunately, although they are from the same charity they are from different fosterers so are unbonded. I think she has done everything right, separating them to begin with, scent swapping and introducing them gradually. They have bowls and litter trays in separate areas and she has a Feliway plug in. But they are still having fights now and again and she's really worried that they will never get on. She's even considered rehoming one of them! Which I think is really sad and too early to be thinking that way. But I'm no expert, I've only ever had one cat at a time. Can anyone offer any advice?

We have two rescue cats, mostly they just tolerate each other and sometimes they actually sleep together, but only when they’ve got full stomachs.

The rescue should never have let her adopt two unbonded cats into the same home. The cats will have arrived very stressed and unsettled and at the height of feeling threatened. And then they are expected to get along! Cats are not naturally sociable with their own kind. They are solitary. I really think she should contact the rescue and let one go back.