As I understand it, kidney-friendly rat diets involve not too much protein, with the protein source preferably being egg/fish/soya rather than red meats, and not too much high-phosphorous grains (primarily oats and certain varieties/preparations of wheat, as far as I can tell – don't worry, Weetabix is surprisingly low in phosphorus, according to the USDA nutrient database). There is such a thing as too little protein and too little phosphorus though (and too little salt, or fat, or any of the other things that are commonly thought of as "bad for you") so unless a rat has been diagnosed with a health problem that requires specific dietary changes, I wouldn't be too drastic with limiting things in their diet just because they're older.
I suspect your girls will be fine to continue on what they've been having – a healthy diet for younger adult rats is much the same as a healthy diet for older adult rats (barring any actual health problems) – but if you did want to make changes, perhaps a higher proportion of 11a would be a reasonable idea as it looks a bit easier on kidneys than the HBB and Arden Grange.
(Incidentally, if you put supplements in wet food anyway, and are ordering from Rat Rations anyway, I personally recommend DailyRat3 instead of Calcivet & Daily Essentials 1. The latter option is convenient for putting in water, but I switched to supplementing in wet food a while back and then realised that DailyRat3 was so much cheaper than the Dr Squiggles combo.)
For older rats that are struggling to keep weight on, fresh meals of easily digested carbs and healthy fats are often recommended (e.g. cooked pasta with a drizzle of olive oil). Fat is very useful in this regard as a gram of fat contains more than twice the calories of a gram of carbohydrate or protein, so it's ideal for getting a lot of calories into a rat with a limited appetite. And cooked, processed carbohydrates are both delicious to eat and easy to digest. So basically all the things that you would want to limit in the diet of a fit and healthy rat because they're very calorie-dense get rolled out for the frail older ones.