In my experience getting the right balance of food for Chihuahuas is no easy task. Because you always have to have their diminutive size in mind. For Chihuahuas, the brand of the food doesn’t matter; your focus must always be on the nutritional balance of their diet.
You need to give them a diet that offers them everything they need, and I’d then suggesting spreading this across the day. By staggering their meals, you give them the energy they need to keep going all day. Because even though they’re small, they use a huge amount of energy. Chihuahuas are incredibly active little dogs.
So little and often is always best, and be careful with portion sizes, as too much is just as bad as too little for such an energetic small dog. To get this totally right, I’d suggest speaking to your vet to fully understand the nutrients they need and how often they need them.