Here is my rating, with comments, as you have asked:
The fast food strip is awful for the following reasons:
1) Too much dialog; you could cut out half of it and you wouldn't lose anything in terms of plot development. In fact, I think your joke is in panel two. Here's how I would edit it:
Panel One:
CK: Good afternoon. May I take your order?
Panel Two:
Blonde: Can I get a burger dressed anyway I like?
Panel Three:
Yowsa! I was talkin' about dressing the burger, ma'am!
(Blonde is changed to Kaddar2 Blonde3)
Then it would be short and sweet. You still get your sight gag with Blonde taking her clothes off, and if you wanted to expand the plot, you do it in your next comic. Or you could get both your sight gags and change CK to Fire in panel three, keep the dialog, and still take off Blonde's clothes.
2) Why is Blonde sitting in a chair at a desk in the first panel? Instead of Kaddar2-Blonde-c-l, you should have used Kaddar-Blonde-2l.
3) The long underscores expand the panel horizontally and mess up the background. It looks like she's standing 15 feet away, behind another cash register from the one at which CK is working.
4) The extraneous dialog in the third panel expands the panel vertically, again, messing up the background. It's like the fast food place was designed by M.C. Escher. (Although, I probably would prefer McEscher's to McDonald's).
As far as "Two caring sisters having a conversation" goes, yes, it was a conversation. No, it wasn't a funny one.
All in all, I give your comics a D. They would have been total failures, but I gave extra points for spelling.