I have litter sisters now aged 11. They don’t really like each other, merely tolerant each other but would be lost without each other.
I have learnt from experience simply not to have toys in the house. Yes, that’s sad but better than having constant tension. Marley is a guarder and will take anything ( slippers, socks, bags, even pieces of paper) and immediately feels empowered . When I spot her with anything I immediately take it away and luckily she will let me. They have become less tolerant of each other as they have got older, it’s seldom that a day goes by without a growling match but it is usually over quickly and doesn’t accelerate.
I do have to manage the situation and this has come from experience. As they both like to present me with a gift on my return home, I make sure that there is more than two objects available so each girl can give me something. Often it will be a dog towel or something similar that I have left out for that particular purpose.
They have become two grumpy old ladies ( something I can identify with too)