Firstly let me say congratulations on your pregnancy. I wish you a smooth journey from here on.
Now I'm going to say something which may be unpopular... I think sometimes we IVFers can forget that ALL children are precious. I do not believe that IVF children are any more precious or loved by their parents than children conceived naturally. Your sister is also a mother of FOUR. Waiting for all four children to be completely germ free might mean she might hardly ever see anyone!! I think you have to accept that you have different priorities ... Yours is getting your precious cargo safely into this world. Your sisters are the four she has already brought into the world and is now trying to get them safely and happily through . She has a different perspective to you. Both of you need to be tolerant of each other's point of view and just try not to get offended by each other for the next year or so.
Unsolicited and unwanted advice comes from everywhere for first time mothers!!! You need to find a way to take what you can use and discard the rest without being too offended ... Otherwise people will drive you mad!!
Just another point of view ...