Best way to control the speed of a group of objects

[zxxz]

Hey, 

 

I am looking to have a bunch of sprites move around and then have a function linking to a button which when pressed halves the x speed of all sprites in the group and then when pressed again returns the speeds to the original value. It needs to work for all objects in the group which may be travelling in different x speeds and in different directions. I have tried to implement something but some platforms are using tweens to move backwards and forwards and I can't see a way to do this with tweens? Would it be better to try and just use the velocity of each object in the group without using tweens at all?

 

Thanks for any help