Bro Vastu Shastra is definitely a Science, but you need to understand this, that it was more relevant at times when there were no other guidelines for construction. Those times, when one would think of construction (which was a costly affair), sure one would like to build it in the best possible manner. One would look for a set of rules to ease the process of construction in a systematic way. Definitely, through Vastu Shastra, all the things were taken into consideration say for e.g. sunlight, air circulation, water source, climate of that particular region etc etc. Saying all this we need to understand that, simply that something that is old or ancient science does not make it "The Best" or "The Perfect".
If you have enough time for research into this topic you will notice Vastu Shastra recommendation(s) are not same at all the places. There are many Vastu Based House plans available on the net and you will notice the plans from the south are different from ours. Moreover I tell you, You cannot make a 100% Vastu compliment house because it is to complex science. There are many many many aspects to it which need to be considered.
My suggestion would be, don't fall into this trap. Once you get into it, there is no coming out of it.
Some nasty people are minting money out of it by exploiting the physiologically fearful souls.
The exception is, Just in case making such changes to the house make your parents happy or gives them mental satisfaction, then let them have it their way but do let them know your true opinion politely.
Believe me, Harmony and understanding among the family members is the true Shastra you need to take care of.
Good Luck