I hate to say this because i know it's expensive but could this be a matter to take to court? perhaps a judge could send your husband to parenting school or counseling regarding how he is handling. this is definitely a serious matter espec the research showing with boys and violence with visual images.
another option, a minister who will sit down with both of you, preferably one he respects. that speaks about your husbvand's love for them.
or maybe your husband is so tired or maybe he does not know how to entertain the kids on the weekends. I wish there was someone he admires who could help him out with brainstorm, or kids same age so he can learn by observing. I find men change very slowly on this stuff and have to watch the effects of good men parenting around them.
another option if he hates church, a person who does mitigations. or else a friend of his, preferably a man, or uncle or grandfather or someone who completely agrees with your viewpoint.
but again the only thing that has teeth is the expensive option. though sometimes you can pay a lawyer to write a "shot across the bow" letter to his lawyer to warn that this is serious and may be taken to court.
I feel for you. my husband just had news on and it took me two years to convince him videos only and even then we carefully screen them. children do not typically understand fantasy v. reality til age 6-8. lots of folks don't know this.