Fingers -sorry, I missed you reply, this thread moves so fast !
If you are already doing 25k per week you will find it easier to move up to the HM training. Even just increasing your long slow runs by 1km each week will soon make a difference.
Ideally to train for the HM you should be running 3times race distance per week, including a long run of nearly race distance or over. So that's 60km per week. Although that would be easier on 4 runs per week than three.
You did 35 last week and could easily do 27 next week and 30 in two weeks.so you are nearly half way there and your race is months away !!!
Just search online for HM training plans and chose one you like that's based on running 3 times per week .then work backwards from your race to get a start date for the training plan . Between now and the start date , just increase you mileage gradually, no more than 10 per cent per week
I always add a few week into the programme, ie I start a 10 week programme 12weeks before race. Then if I get injured /sick /kids get sick /on holiday I can accommodate it ok.
I understand about the school holidays BTW, I can only run in term time as my DH works away a lot . That's why I only do spring races, autumn in hard with the long summer holidays . Of course, a good mother would enjoy spending time with her little darlings, rather than looking longingly at her running shoes ....