It is normal for a child to tell fibs about things like that and at 7 still your responsibility to ensure they are done.
A reward system may help, harsh punishments will only create further problems.
Frankly your husband would be better off getting of his backside and supervising teeth brushing/homework. What he is doing isn't parenting in any way, its lazy, neglectful and emontionally abusive and I think you should look at why your husband treats his son so badly and demand he gets help or leaves.
