Defiant and Unaware seem like the best offensive options, as Deck Knight above me mentioned.
Defensively, Levitate seem like the better option in that it deals with the Ground-types that still give the core problems. CAP18's weaknesses of Rock and Electric are both alleviated with Lucario and Latias' resistances to those types, meaning Filter is not necessary to handle those common attack types. Regenerator could be considered to allow for free-formed switching with Stealth Rock and Spikes up, letting the trio handle those hazards well enough to not have to run Defog on Latias, but I fear that it otherwise has too much utility of its own. Bulletproof makes it hard-counter Aegislash outright, but again I fear for similar reasons to Regenerator that it might make the CAP18 independent from the core entirely.
Defensively, Levitate seem like the better option in that it deals with the Ground-types that still give the core problems. CAP18's weaknesses of Rock and Electric are both alleviated with Lucario and Latias' resistances to those types, meaning Filter is not necessary to handle those common attack types. Regenerator could be considered to allow for free-formed switching with Stealth Rock and Spikes up, letting the trio handle those hazards well enough to not have to run Defog on Latias, but I fear that it otherwise has too much utility of its own. Bulletproof makes it hard-counter Aegislash outright, but again I fear for similar reasons to Regenerator that it might make the CAP18 independent from the core entirely.