With any change in diet gradual is best.
The diet of dry food you are giving them would be nutritionally sound. I think dogs enjoy the change of texture on their palate, and the inclusion of fresh food also helps to increase their variety. This is not from a nutritional viewpoint, a pleasure viewpoint only.
It is not mentioned what proportion of their diet you want to become wet food. For the purposes of how to introduce the change it doesn't matter, as the process is the same.
Break each feed into two subset feeds. It takes a little longer to feed them, but will assist in making the transition work smoothly.
- Mix one quarter of the dry food for one feed (1/8 cup) with two scoops of wet food.
Feed this to your dogs. When they have finished eating add the remaining dry food (which will be a total less than 1/2 cup) to the bowl.
Do this for a week. In this time you can monitor their stools, as the introduction of can food is likely to make them more watery if any change is going to occur.
If the stools are consistent and healthy. Increase the increment.
- Mix half the dry food for one feed (which would be a less than 1/4 of a cup) with 4 scoops of wet food.
And repeat the process. Increasing and tweaking the balance of wet and dry food to manage their weights, until it can be served as two meals with no subsets.
Technically these amounts could be broken down into percentages or actual volume, weight, however, the general process is not too hard to follow. As they are only little the incremental increases seem small, but in reality the principle of proportions would be the same for a larger dog.
As you are probably aware, there are senior mixes for your older dogs and different products to suit different dog types.
It is important not to mix wet and dry food that is not consumed in one sitting. As the wet food moistens the dry food, and left for hours, this can breed bacteria. Unless being consumed immediately, I always serve wet, dry and fresh foods in separate dishes.
A note about teeth, raw bones are good for cleaning teeth.
I plan to purchase the pet food soon; my gut instinct is to purchase some wet Science Diet brand food if it is available.
The good Guide rated over 300 wet dog food products.
Best Wet Dog Food Ratings
Science Diet Adult Advanced Fitness Gourmet Turkey Entree
Cesar Gourmet Filets Filet Mignon Flavor
Purina Pro Plan Beef & Brown Rice Entree Classic
Purina One Healthy Weight Wholesome Entree
Iams Veterinary Formula Intestinal Low Residue, Canine Canned Formula
I am not endorsing these products just offering findings from some market/science research.