Personally, I did not find getting a second to be that much work than owning one on a day-to-day basis. The main differences are obvious: more expense, more messes, and more trips to the vet. Getting someone other than a kennel to watch them is also much more difficult when you have more than one. We don’t use a kennel, so we have to have REALLY good friends to watch both, since we have no relatives we can even ask who live within 400 miles. And we have been totally unable to set up a mutually beneficial Yorkie (or any small breed) pet watching share situation, even after attending several local meet ups (the ladies already had their sitting relationships defined long before we arrived on scene). So please do not discount the difficulty of finding others to watch two vice one; you said yourself that your parents will not be keen on watching two. If you plan to depend on their services you had better work that out in advance.
Also, don’t expect that they will keep each other company when you are around and need to study. Mine will play together at times, but more often than not, they are in competition for your attention and affection. This is especially true if they were not littermates I believe. For example, mine like to play fetch (one is totally addicted to it) and they just get very upset if there is only a single toy to play with, instead I need to keep playing with both with 2 separate fetch games at once. Each has their own toy of interest and seems to pay no attention to the other when in a fetching frenzy. That is the main reason why however much I love Yorkies, I would never get a third – I only have two arms and EACH demands attention like a belly rub and will fuss if I don’t pay attention to both at once.