Normally, I wouldn't suggest feeding something underneath the quality of EVO or Solid Gold, if it's in your budget, and if your cats PREFER it, and has proven to do well with it. And I do applaud you in your quest for finding a healthier diet for your cats...BUT, for Tom (the senior kitty), I would stick to what he's been eating, and what he enjoys. At his age, quality of life is very important, and if he is turning his nose up to the EVO or Solid Gold, and enjoys eating the Whiskas, and has done well with it in the past, I personally would stick with it. At Tom's point in life, he should LOVE what he eats, and thoroughly enjoy each meal, even if...well, it's kind of crappy. Do you kind of get what I'm sayin'? That's really not my usual advice. Part 2 of my advice will tell you that Tom needs to be fed separately, since he's been known to "hog" Bindi's bowl too. Feed him where he normally eats, give him 30-45 minutes, if he doesn't finish, time to put the food away. Bindi should be elsewhere during this time, perhaps in another room, being fed his own meal separately. The 30-45 minute rule applies to him too. They should quickly learn that this is mealtime, rather than nibbling, and walking away.
Part 3 of my advice...don't mix foods together. I know you feel like it's giving Bindi and Tom the best of both worlds, but the truth is, you're looking at creating a nutritional imbalance. Now, that being said, I'm all for feeding one brand of dry (such as EVO), and another brand for wet, such as Solid Gold...for two separate meals. This would be fine.
Individualize for each cat. If Tom prefers (and is maintaining good health) on Whiskas pouches, so be it, and don't stress too much. If Bindi will thrive and accept EVO or Solid Gold, that's wonderful!
About feeding raw...there are tons of web sites out there, and if I attempted to post any of them, they'd leave your head spinning with information! And then, you'd have to sift through the good raw sites, from the ones that aren't entirely accurate, and each different raw feeder's perspective, methods, etc. Blah!!! It's awful to research raw feeding online, as I've done it before, and there is a lot of misinformation out there, unfortunately. The best advice I could give you would be to pick up Dr. Pitcairn's book on natural pet care, or actual literature by Dr. Billinghurst. Now, at least these are sound professionals with research to back themselves with.
My last comment, is that feeding raw is probably almost (again, depends on the cat, and their needs...there ARE some cats that do not thrive on a raw diet, due to pre-existing health conditions, genetics, taste preferences, etc.) always more biologically appropriate and healthier for cats...they're carnivores, and weren't designed to feast on meat-flavored cereal, and unfortunately, EVO and Solid Gold are still processed, commercial foods...as healthy and nutritious as they are for cats, they are still cooked, and the idea behind ANY kibble is far-removed from what your kitty would be eating while exercising their true carnivorous eating behaviors.