What is your advice to me and my husband, who does not spend on me, my household, and my children sufficiently, knowing that he is financially capable?

A husband must spend on his wife and children equitably, as Allah Almighty says: "And upon the father is their sustenance and their clothing according to what is reasonable." Sustenance according to what is reasonable is estimated by sufficiency, so a financially able husband is obligated to provide his wife with enough food and clothing appropriate to her status and the custom of her peers.