Yes. That would be proper, after all, you are not getting married.
The family of the parents, perhaps some of those people who officiated at the wedding (bridesmaids / best man etc) and the children of the parents.
All gifts should be returned if the wedding is called off regardless of who called it off.
There are many things that can be written in a wedding card from parents of the bride. The letter should include well wishes for the marriage.
If the parents are deceased, she should ask a lawyer about it.
Anything you or the grooms parents feel comfortable with maybe a honeymoon present. If they step in too much just ask them who's wedding is this
Well they are your parents the invitation can say daughter of
The groom's parents are only responsible for paying out of town guests at rehearsal dinner for: Parents of the bride (some parents are divorced and one ex may live out of town or both live out of town, but often the out of town parents of the bride will pay their own way if they can financially afford it); Maid of honor; bridesmaids; flower girl or ring bearer. Any other relatives or friends that are not in the wedding party should pay their own way.
You should probably skip that and go to their wedding. Remember family is much more important.
No way...
When going to the church the mother and father of the bride along with the maid of honor; brides maids; flower girl can go in the limo, but after the wedding is over the bride and groom if going for pictures first should leave the church on their own and the parents from both sides of the family along with the wedding party should meet the bride and groom along with the photography at a designated area for wedding pictures.
The slaves should be freed because they were kidnapped and sold into slavery because their parents did not care.