I have practiced real estate law in the Bay Area, and from what you are posting I can tell you that you really need to speak with a local attorney prior to closing your escrow. (I know customers don't come to this site to be told "go hire an attorney" but please let me explain why I am giving this advice in this particular instance).
You are buying in with less than 25% ownership (so an Owner Move In ("OMI") isn't going to work for you (see: http://www.sfrb.org/index.aspx?page=965). You can try purchasing additional shares or interests from your new neighbors, but there isn't a way to "borrow" an additional 15% in order to bridge the gap - if you do try to do this, proceed with caution and with legal counsel.
You can try buying the unit and then doing a lease termination and pay the relocation expenses. You must follow the "Ellis Act" precisely (see: http://www.sfrb.org/index.aspx?page=966), again, I recommend caution, and legal counsel (as a precautionary measure to ensure you meet these requirements).
But, regardless of how you terminate the tenancy, evicting a tenant can affect the lottery for the conversion of the TIC (see: http://www.andysirkin.com/HTMLArticle.cfm?Article=2), so you must again be careful here.
Bot***** *****ne: it is possible to move into your new home, move out the new tenants (although you may have to pay them), and have the TIC conversion. But with the numerous steps and specific issues that must be addressed, it is simply too factually complex for me to tell you on this forum how to proceed (we can offer "general legal information" but cannot provide you with "specific legal instruction" which is what you really need here).
You can find local landlord tenant attorneys (there are many in SF and Oakland familiar with the Ellis Act, using the State and local Bar Association directories (the BASF directory is excellent), or private directories such as www.AVVO.com; www.FindLaw.com; or www.Martindale.com (I personally find www.AVVO.com to be the most user friendly).