Ranking questions

I have a ranking question on brand awareness, with 8 brands listed.
a. If a respondent only mentions say 3 brands, the question shows an error, requiring that all the 8 options should be ranked. Is there a way, apart from, say limiting the choices to top 3 that I can use to leave it open? Since the number of brands respondents are aware of may vary.
b. I want the next question to capture only those options that have not been mentioned in the ranking. Is there a way to do this?

@Impact123, maybe this post discussed previously should help you solve your issue: