The kittens are only five months old aren't they? Not six months. So there's no desperate hurry for the snip. I'm so sorry if I worried anyone, I miscounted! It seems like they left years ago, it really does. *sigh* Give them all a kiss from me please!
They can be 'done' now if you like though. Only you know your kitten, and what the right time is for them. Standard advice is 6 months for a girl and 6-8 months for a boy, although I wouldn't leave it as late as that for a boy to be honest. The earlier you have it done the easier it is on them anyway- Sulley just had his done and D reports he was running around in his usual bonkers fashion afterwards. It's a bit more involved for girls, but even then if its done at 6 months its no big deal.
Of course if you have a boy who starts being much more aggressive all of a sudden, develops suddenly very impressive genitalia (my goodness have you seen an unneutered Tomcat? I'm surprised they can walk!) or even *horrors* starts backing up to surfaces and waggling his tail about (spraying, some kittens go through the motions of spraying before they actually spray) then that's a very big hint that you need to neuter him ASAP! And if your girl goes into heat you'll know all about it. Tonks can do this at 6 months, so don't leave it too late!
But you have a few weeks. I'm sorry if I alarmed anyone... silly me!