All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
The situation is as you read in the Fatwa which you referred to in the question that it is permissible for the husband and wife to play the Duff (a tambourine-like instrument without bells). What is meant is that the wife is permitted to play the Duff when singing to her husband or dancing to him. As regards the husband playing the Duff, then the scholars prohibited it, and this is the most preponderant opinion in our view (in Islamweb), but some scholars permitted it for the husband as well.
However, you should know that it is permissible to play the Duff but not other musical instruments as these are forbidden.
As regards some of our Fataawa in which we mentioned the cases of marriage and birth giving feasts, then this was just to give examples of occasions where the Duff is permissible but we did not mean to restrict the permissibility of using the Duff to the above two occasions.
Allaah Knows best.