Hello, Rochelle,
Hands-down, I can't say enough positive things about the accommodations Walt Disney World makes for speciality diets. For a time in my life I followed a vegan diet (no animal products). While at WDW, I
never had any difficulty dining. In fact, at nearly all of the table-service restaurants the chef came to speak to me about possible entrees and often made food to reflect both my needs and tastes. I truly felt like a princess with all the special attention and assistance.
To help convince your brother, just let him know that all that needs to be done is to include a notation in your dining reservation at least 24 hours in advance (you can call 407-WDW-DINE). You can read more about Special Dietary Requests
here.
Also, my friend Disney Dad Jonas along with help from Disney Mom Deborah have gathered some helpful information to help guests keep Kosher while at WDW that you can read about
here.
I hope this helps to sway your brother; please let us know if we can help further. I'm keeping my fingers crossed!