Requesting contribution from adult child

[hidinginthebathroomagain]

DH and I live with 2 DC. Aged 21 working FT and early teen.
DC 21 only pays his phone bill all other wages are his own. DH are always skint. Account is almost empty a week before payday. We have 5k in loans for house repairs. I feel DC should be contributing but DH is reluctant.
Bills come to £1300 plus shopping and cleaning products etc. I think £300 is fair DH thinks £100 which I think is pointless. His washing is done, food made most nights and bedroom cleaned etc. His GF stays her around 3/4 nights a week too which is increasing costs.

is £300 too much? He probably has £1600

I also don’t charge rent. ds does own washing mostly, is starting to do more in kitchen, especially on day off, and stays at GF 2-3 nights/week. However it’s getting tight and he’s offered to pay rent. I’ll ask for £100 /month and try to save it for him.