How money can i give my son and this wife tax free in one tax year.

Surely you're not suggesting tax-avoidance Noddy1? If twestb has sufficient savings to declare them on his annual tax returns then the Tax Man will wonder what he is doing with his money if he cant account for where and what he's done with it. Trouble ahead there me thinks!
But twestb can give 5k each to his son and daughter-in-law per annum but again they need to declare it on THEIR tax returns as extra income as this might effect their personal tax position/allowances. Roseangel is correct about the 7 years for inheritance tax as many people would try and hide parents' savings if they need to go into a care home or have a financial assessment for care costs. So its a gamble whether to pay 1 tax or another, but Id never advocate not paying as the tax man never lets go once he has his eye on you!