The most important thing is to figure out their living situation, considering both are largely aquatic pokémon. This would be a bit more complicated due to the average spheal’s need for slightly colder waters than what a dratini can handle, except it seems your spheal is strangely acclimated to warmer temperatures. (It may be worth it to see if anyone had lost track of a dratini and a spheal by taking yours to a pokémon center, but given their eagerness to be with you, the answer to that question isn’t quite as important as it would normally be in situations like these.)
Thus, you only need one pool, but be sure to make it large enough to accommodate both a dragonair and both of spheal’s evolutions. Dragonite are not quite as reliant on water as its previous forms, so you don’t need to be concerned about space for one. However, walrein can get pretty large, and their space requirements can potentially get rather demanding, so be sure to place this pool outside if at all possible. I would also recommend keeping a close eye on your spheal as it evolves, as its temperature requirements can also shift, and dratini and dragonair—being members of an evolutionary family that isn’t quite as quick to evolve—may not be able to handle the temperatures walrein needs. If your walrein can handle warmer climates as your spheal can, however, perhaps this won’t be as much of a problem. Alternatively, if your spheal’s special ability is Thick Fat, then you won’t need to worry, as this is the likeliest explanation behind its ability to tolerate warmth.
That aside, once you figure out where they’ll be homed, be sure the pond or pool you construct for them is always supplied with fresh water. Also be sure to have a source of drinking water (such as a nearby water bottle), as pokémon should never drink the water they live in. This is, after all, where they will normally relieve themselves. On that note, also be sure to clean the pool or pond as often as possible—once a week at the absolute minimum. Install a filter system to take care of the days in between cleaning, and be sure to test the pH levels each time you clean.
As for food, both are carnivorous and feed primarily on fish. Don’t feed them canned tuna, as this can be too fatty for them. Instead, try to secure salmon or tilapia, but cod and bass will do just as well. If you absolutely cannot afford fish, you may be able to feed them with chicken, but by then, you might as well just give them kibble. For their spheal and dratini stages, food should be cubed, but as they evolve, they’ll gain the ability to handle whole fillets. If you’d like to give them treats, both can eat shrimp, and some people like to give their spheal squid or octopus if it’s available in their region. Additionally, dragonite become omnivorous and typically eat a wide variety of foods, including fruits, vegetables, and meat from land animals in addition to seafood.
When it comes to grooming, both will largely self-groom, especially thanks to their pool. Dratini will shed their skin now and then; simply provide a nice, flat rock for her to crawl onto and rub herself against during this process. Be warned that she may turn defensive towards her spheal friend for a few days during and after shedding. This is completely normal and comes as a result of the fact that pokémon that shed have softer skin that’s not quite as resistant to damage for those few days after their upper layer has been shed. It takes a few days for their new scales (or exoskeletons or what-have-you) to harden or toughen to the consistency the old layer had. This will typically happen four to six times a year for dratini, so if it’s been a couple of months since she last shed, you may wish to prepare (by informing your spheal and keeping her away from her friend for a bit).
In terms of entertainment, spheal enjoy anything that they can balance on their noses, particularly round objects. (Some behaviorists believe they also like round objects because spheal see themselves in them, so it’s much like playing with dolls for humans.) Supply your spheal with plenty of these, and she’ll be happy. Your dratini will likely play with anything you give your spheal; dratini aren’t particularly discerning when it comes to toys.
As for sleep, neither really need beds of their own, and because spheal are warm-blooded, you may not even need a pool heater for your dratini. It may be a worthwhile investment anyway, though, particularly for colder months, but if you do get one, be sure to test it out by observing how your spheal reacts to it. If the water is too warm for your spheal, simply provide a nest of blankets for your dratini to crawl into at nights or bring her inside and allow her to sleep in your bathtub.
Finally, training. Be warned that it may be tricky to train the two together, as dratini, until they evolve, rely largely on physical moves. This is a problem because your spheal’s mainstays are colder moves that could do serious harm to your dratini if she gets caught in them. Thus, it’s wise to train them separately and to use them for single battles, not doubles. Alternatively, use TMs and be extremely cautious when training your pokémon in tandem.
Best of luck, reader, and congratulations on your new pokémon!