DH is a pastor so he can't/won't baptise his own child, so we will be having it done at my home church where my family attends. We aren't sure when yet. We will invite close family, our parents grandparents and siblings only. We will probably just have a little cake after the service. No big party for us.
I think if you said to your family that you are having DS1's birthday party and since they will all be around it seemed like a good day for the baby's baptisim, it doesnt make it tacky it just sounds to me like you are trying to make life convinent for everyone.