Has the shop owner received a 3-day notice to pay or a summons and complaint? If he does not pay the rent to the landlord, you can all be evicted. You may want to talk to him and/or the landlord about taking over the lease. You can add yourself as a defendant in the unlawful detainer (eviciton) lawsuit by filing a pre-judgment claim of right of possession with the court.
This is not legal advice or create an attorney-client relationship. This is merely a discussion of general legal principles; the nature of this communication is such that not enough information is available to give specific advice. If you want further information, you should contact a lawyer with experience in your area of interest.