Townhouse foundation dilemma. Advice needed.

Need advice. We own a townhouse near the Med Center built in 2006 now needing foundation repair. Because we share a foundation with 4 other townhouses, all 5 owners have to agree (and pay for) leveling. 4 of us are signed on, but the 5th is totally MIA. That 5th owner rents his place and the property management company can’t get a hold of him either. We’ve been trying for 4 months. He replied only once, asking if the city is liable somehow because street repairs have been done (clearly, they are not), but that’s the one and only time we’ve heard from him. We understand the repair company can simply stabilize without all 5 signed on for a full repair, but that seems like a last resort.

What are our options? Is there any sort of legality that we can utilize? Has anyone else faced this?

Any advice is appreciated!