if I book & pay for 2 flights with emirates for my son & his girl friend,will I be able to claim the airmiles to my Skywards account. They will be of no use to my son.

you would get a family bonus, but only for 20% of the miles flown.

quote from the skywards website rules:

"Every time you fly you will earn one Skywards Mile for every mile flown, which is then credited to your account. You can also take advantage of the Family Bonus programme offered by these airlines. Simply nominate up to eight family members and when they fly Emirates or SriLankan, 20% of their flown miles will be credited to your account, including bonuses for flying Business or First Class and any promotions."

so I suggest to set up an account for your son, maybe you can use the miles for youself (upgrade) one day? I had the same problem when I booked a flight for my mother and her boyfriend - I set up accounts for both of them and used the skywards miles for an upgrade later. But the situation was a bit different, as they got a lot of extra promotional miles...