Hi
Woman lives alone terminally ill and in receipt of DLA etc with SDP. She has a grandson who is willing to stay each night to watch over her. He will only be there at night. He is a student now 17 but will be 18 in June. Will SDP stopm in June

The issue will be whether he is a non-dependent who resides with her. That will be a question of fact. Will he stay awake at night so he can watch over her (which is what "watching over" implies? Will he be in her bedroom or in a room of his own? Will he take or make any meals there, bathe there, keep clothes there, do any shopping, washing or general cleaning? Where will his "home" be?

As in any case involving the issue of whether two people are members of the same household, it will boil down to the facts of the arrangements.

and even if he did move in to care for her, and be "normally residing" with her, the first 12 weeks do not count so long as it the first time he has joined the household

Does he have another address, if he does then it is a strong indicator that he is not her non dep.