Advice on adding a newbie where a cat already resides

[Stilllivinginazoo]

So we lost our darling boy atticussuddenly 5weeks ago
His brother was distraught fir a few days checking rooms and mewing, even though they weren't esp close (rarely slept together etc)as a rescue pair they'd never been apart.he was 6 .fast forward and whilst dd2(atticuses main squeeze) is adamant she doesn't want another let of her own lil zoo has ask if we might get another cat.
His brother is neurotic,and prone nervous chewing,esp if smells toms. this has all stopped now he's an only(he's goes out minimally).I've asked friends with multiple pets and they think a girl kitten may be tolerated.I need some good old mumsnetters experience on how to proceed...

So he's happier now he's the only cat?.

He's a bit more easy going,but hard to tell if that's because he has total dominance over our indoor space or because doesn't feel need go out and see what's going on as much(as brother was out)if you see what I mean.there are a LOT of Tom's vie top cat position in my garden,lots spraying etc....(any advice on that offered I'd be grateful fir too as can't put washing out as gets sprayed on)

I would wait. Your cat seems to do better as a single cat, but also for your DD. It's still recent and she might need time to grieve.