Kungfu I think your text back to your sister was perfect. I'm very impressed with how you turned his demands into him being sweet and helpful.
You are a wise woman.
However as you've beat him on this level I'd expect him to sink lower. I think it's clear he's trying to dominate you by "demanding" (via your sister) a greater status in your family. Frankly we both know that would have to be earned but emotional cheapskates like to be given a lot for little or no effort.
If I were you I'd try and exhaust him. Keep your sister close. This will mean talking on the phone to her rather than text so you can be sure it's her. I know he'll probably alway answer so use the opportunity to talk to him. Do the same thing you did in the text. Assume all his words are kind and interpret them so, alway knowing he's a conman. Hopefully he'll be hitting the sweetest, most kind natured brick wall. He'll get frustrated and show his true self. Hopefully in front of your sister.
Keep us up dated and congratulations on your wedding!