Congratulations!
One thing to consider is that you need to make your sobriety as your #1 focus now. Having a "party" with your brother and sister-in-law during your second week of sobriety might be more of a test than you need to subject yourself to.
I agree that you can certainly have fun at a party with others drinking (and you not), but I found that I did need to build up some of that sober bank account before I could attempt it.
From my experience, I tried to change the venue a bit when this happened to me.
First, I was honest with everyone that I wasn't going to drink. I planned what I was going to say ahead of time - and I told them before they arrived. Honesty is best, but if you aren't ready for that (as I wasn't), you can come up with something vague like "Alcohol just isn't working for me now, so I have decided to take a break for a while." This allows them to make alternative plans if drinking is a big deal to them. (If it is, this is a red flag to be discussed at a later date.)
Then, while I did have a bottle of wine for them to drink at dinner, I got rid of all the extra alcohol so they wouldn't be able to drink for more than just the dinner time. Coffee with chocolate is pretty good for after dinner.
With all this said, there is nothing wrong with asking everyone not to drink while they are at your house. If your sobriety is your #1 objective, then your guests having a slightly less-fun time is not your concern. Send them to the local bar/restaurant while you go to an AA meeting or such.
I am thrilled that you are so committed to be completely sober when your relatives come and still have fun. It is a great attitude. Just also recognize that you are human and you need to take things one day at a time. There is no reason to "test" your will power un-necessarily in these early critical weeks.
And you might be surprised, they might be thrilled to see you not drink (and you might even lead by example).