I so agree with Barbarian, and start getting them to make things for each other. A house full of secrets and surprises is brilliant. Eg, we used to make
A pretend cracker using inside of foil roll or equivalent, wrapped and filled with cheap sweets and a car or so from the charity shop
A pasta necklace fro the three year old, or a button string,
A decorated box for mummy or siblings
A decorated picture frame for daddy / granny card ( inside if cereal packet, cut out) decorated with drawings, or painted pasta, or a coloured paper napkin
A calendar, you can buy those small calendars fir v little, then with a drawing attached, grannies and dads love them or say they do
A desk tidy, loo roll inserts, on card ( those cereal packets again) covered with paper
Peppermint creams, icing sugar, White of egg, peppermint essence.
Fudge.
Plan your Christmas Day, ( if you're that way inclined, a Christingle service or singing riund a local tree is fun the day before. Decorate the house, paper chains, scour the charity shoos etc for discount artificial trees. Make decorations, biscuits, angels from foil or paper. We have a superb huge paper angel playing the guitar, made when DC was 8. Brilliant. Comes out every year, wouldn't be Xmas without it) . Stocking opening, walk or present opening, , lunch, present opening or walk, tea, tv.
Boxing Day, board games and walk. Make pancakes for special. Make popcorn. Hide and seek/ sardines. The potato game. Followed by exhaustion and tv. If you've got a BBQ, have a winter BBQ and toast marshmallows at it. ( baked potatoes already done, sausages nearly ditto, everyone wrapped up, toasting marshmallows. )
For stockings, I used to do: clementine in the bottom, magazine rolled up ( takes up lots of room) , cheap set if colours from aladdins cave/Morrisons ( cheaper than Poundland) and a pad, toy from charity shop, sweets and bubbles to blow, possibly some bubble bath. Average cost £5-6 dep on magazine.
I never spent more than £20 on Ds, apart from stocking, say £3O now in part because his birthday is just before Christmas. If he wanted something I'd just say we need to save up for it. He understood.
You'll see, they'll think it's the best Christmas they ever had. Tell them that instead of things, and you can tell the older ones that money is tight, you're going to make your own fun. They'll be great. So will you.