You are in a fairly unique situation. I would recommend posting your profile and desires in the admissions consultants threads and seeing what they say.
From what I know, here is some advice:
1) Out of the top schools, I know that Kellogg has a huge push for getting people that are involved in family businesses. They even have a Center for Family Enterprises:
https://www.kellogg.northwestern.edu/res ... /index.htm2) If you plan to take a hiatus from the family business for a couple of years and then return, you may be wise to either work for a top management consulting firm, or for a leading company in your industry in a general management position (I'm not sure if there may be conflicts of interest here). In order to do this, you may want to attend an Ultra Elite or Elite school.
3) Don't underestimate the value of a top school pedigree for running a family business. I feel that employees, investors, customers, suppliers, etc. will all question your age a little bit when you takeover, but it will be far easier to ease those concerns if you have a top school and maybe a top MC firm on your resume. In the end, your school name is not going to matter as much as it would for someone going down the corporate path - but it may have small side benefits. If you end up deciding to raise institutional capital from private equity or venture capital firms to expand the business - the top school pedigree will pay huge rewards.
4) Any school that has a solid entrepeneurship curriculum should suit you well. Obviously, you will want to take courses like Entrepeneurial Finance, Operations Management, New Product Development, Leadership/General Management, etc. and you won't particularly care much about a heavy finance curriculum.
5) This is probably something you need to ask others and admissions consultants about - but in your goals essays, I think it would flow fine if you mentioned the short-term goal of MC and then a long-term goal of working in the family business. However, you want to ensure that you lay down some concrete ideas for what you plan to do with the family business (transform it, revitalize it, expand it, etc.) so that you give off an image of someone who is very ambitous and someone who is going to make an impact. If you can tie your goals for the family business with social impact/do-gooder type stuff, even better. You just will want to make sure that you don't come across as someone who plans to takeover a middle-market business, not do a whole lot, and collect the dividends. These are all my personal thoughts on positioning and they should not be taken as professional advice or gospel - just simply what I would do if I was in your shoes (from what I understand about your shoes).
Good luck!