RE:These Mexican litigatorsOf course Exn can be forced to pay. it is basic Law 101. A judgementr entered against a subsidiary can be endorsed against the parent company. As long as EXN owes the majority interest in San Pedro, any litigant with a claim against San Pedro can have the judgement endorsed against the majority owner.
Anything Exn tells you (in this case that Exn does not "believe" the winning litigant can satisfy its claims against the parent) should be taken under advisement