How will kitten take to new brothers and sisters.

I took on a cat  which unbeknown to me was pregnant - she gave birth to kittens 16 weeks ago. I have kept one kitten and rehomed the other three. I took mum cat to be spayed approx 2 weeks ago to be told by the vet that she was approx 4 weeks pregnant again. She has become aggressive towards the kitten that I kept - she was grumpy and short tempered with her last pregnancy too.  One of my concerns is how the kitten I have will react towards the new kittens - he is male and as yet un-neutered - I was going to wait until he was six months.  I am worried he may be either aggressive toward the new kittens when they arrive or overly playful and too boisterous for them. He is very affectionate with me and seems shocked that his mum hisses and spits at him though I suspect that she is just protecting herself. There is no aggression from him towards her. I am unable to put them into separate rooms as I live on a narrowboat. Does anyone have any experience of this sort of thing. Would be grateful for any help/comments. Am I worrying about nothing?

Thanks.

It's natural for mama cats to try to chase away their older kittens before the new batch comes. I think I would have him neutered ASAP---she may feel less threatened by him after he's neutered. he may be more inclined to feel big-brotherly to the kittens, and also to prevent him from getting her pregnant after this batch, because he's old enough to be fertile now. And keep her inside until she's spayed, or you'll have a never-ending cycle!

Mum gave birth to 5 kittens almost two weeks ago. I have to say the older kitten so far has been very good. He is still a month off being neutered so I do have to keep a careful eye though. He does try and help wash the new kittens bless him - I think he wants to play but they are too tiny yet. Mum cat is in a much better mood all round now she has had the kittens.

tx for the update.  splendid they are all friends, and he is trying to be a help mom as well as he can.  This is not unusual,  neutered or not yet.  but good he is.    Good genes!   

Why do you want to wait for the 6 month?   I know in some countries this is the recommendation. so also in sweden at this moment (it was one year several years ago).

But the practice in USA and other coutries shows  there are no problems with earlier spaying / neutering.  Some vets feels even it is actually easier to spay them earlier, they do heal beatter.

good luck!