Used to use this forum years ago and you were all so helpful, I'm hoping for help again now. This is going to be long so please bear with me.
I have 2 lovely cats, Lola and Dexter, unfortunately anytime they are in the same room together they end up tearing strips off each other

For background, We had 2 cats Charlie and Harry - brothers we had from kittens. Harry sadly died of heart failure aged 3 in 2010, so in early 2011 we adopted Lola from the RSPCA. We slowly bonded Charlie and Lola and they became friends, playing together, eating together. Complete success. Our daughter arrived in 2013, Lola sadly was not happy about this and wouldn't be around if our daughter was, but used to come in in the evenings once she'd gone to bed. Sadly Charlie succumbed to heart failure in 2014 and a month or 2 later we moved house.
Lola adapted to being a single cat well, but still won't be in the house if Imogen is awake. So we were missing Charlie's companionship, so we bought a main coon kitten in May 2015 - cue Dexter. Hes fabulous, he is a soppy lap cat, very patient with our now 3 year old, joining in tea parties etc. Naively, because all had gone so well with Lola and Charlie we assumed she'd have no problem accepting a small kitten. We thought wrong

We've had Dex over a year and other than the odd hiss if they cross paths it hasn't been an issue. I naively hoped once he was neutered (breeder said not to do him before 18 months) and he was going out too that the animosity would die down. Sadly its got ALOT worse.
Dex was neutered a month or so ago and we started letting him out. This week they have had 2 nasty fights, one at feeding time (we feed them separately) and then this evening. Lola actually came in this evening, which was lovely. So she was curled up asleep on the sofa with us. Dexter came in and just went nuts - they both ended up rolling around like one ball of fur, fur flying everywhere and Lola has split his nose open.
I bought Feliway Friends last week and Lola is definitely more chilled, but Dex as I say is worse

What can I do to stop the fighting?? I've given up all hope of them being friends, I just need them to tolerate each other. This is a 3 story 4 bedroom town house, there is plenty of room for them to coexist!!