Hi Lena. I am so sorry to see that they rejected your spousal case, however, very happy to see they are giving your husband a TRV to return to Canada based on his work permit.
I would suggest, rather than appealing the current case, to fill a new application (provided the fees are not a big issue for your family) and be sure to include everything you previously did as well as any current photos you are able to obtain of you and your husband from other friends and family.
I don't feel that the VO was correct in his assessment, but I can see how he might have questions. I did not realize (because I didn't read your background) when you asked originally that you were a same sex couple. I don't think it would've made a difference, excepting in the fact that you were previously in what they would consider a heterosexual marriage which included children. Based on that information, I would've expected them to question your current relationship a bit more closely, only because that is not a typical situation.
Please don't misunderstand me, I don't at all doubt the genuineness of your love and commitment to your husband, only explaining to you what someone on the outside might see.
Knowing this information, I would suggest you try to think about what you would say and/or do to speak to someone from that perspective to convince them that your relationship is real and true. Maybe go into more depth about why and how your previous marriage didn't work out. Maybe explain how you felt being married to a woman and how you knew it wasn't right, but maybe it was expected from your family or the way you grew up ...
I'm just rambling now, but please, if you need assistance trying to figure out how to overcome this, and you CAN and WILL overcome it, don't hesitate to ask.
Best of luck to you and your husband!