Plumbing Issue - Landlord's vs. Tenant's expense

[Chan Park]

Hi BP community, 

My tenant, who lives in a two-story, newer construction SFH complained of a water leakage in the bottom floor kitchen ceiling (through the LED lights). Upon tenant's brief inspection, he thinks that water is leaking from the 2nd floor restroom showers.

I sent a plumber the very next day, who said that the caulking is completely gone in the showers and that it needs some good caulking and call it a day. Tenant caulked the bathroom w/o any issues and did not hear from him for about 10 days.

I get another call last night. Tenant said there's another water leak and he thinks that it's coming from the 2nd floor restroom again. Sent another tech from a different company to get a 2nd opinion. Upon inspection, the tech said the tenant's younger son actually let water overflow while brushing teeth, which led to water finding its way down to the bottom floor ceiling. The plumber removed the debri built up in the sink, which could've help cause the water overflow.

But THIS is when things get interesting. So the water damage in the ceiling remains. I'm trying my best to prevent mold growth, so I asked tenants for their renters insurance, to which he said, "our renters was with geico and we just switched insurance providers this month and have not got a policy active yet." 

We have a renters agreement, which states tenants shall be held responsible for all costs to landlord's repair or maintenance of any plumbing stoppage or slow-down caused by tenant. AND an agreement to have a renters insurance. It also states if they allow insurance to lapse, "the same shall be a default of this lease." 

TBH I don't know whether that means I have the right to expire this lease or they're completely responsible for all expenses.

I like my tenants, they're always paying on time & communicative. They've been w/ me for a little over a year. But NOT having renters insurance and allowing water leak is not OK in my book.

The water damage in the ceiling appears minor (to the naked eye). But we just don't know how extensive the damage is on the inside. 

Should I use my homeowner's insurance policy to cover the costs? How would you go about this issue?

Thanks in advance for your input and knowledge.