Are we crazy to consider having a third child?

My husband and I have been discussing having a third child since our second was born 2 1/2 years ago. We also have an almost five year old.

About six months ago we found out my sister and brother in law were trying to start a family. They have been through a lot, but with some help, they were able to conceive and are due in the spring.

My sister in law is also expecting, shortly after my sister. This will be her third as well.

We would to add one more to our family. We think this would be the best time bc we like having our kids relatively close in age and we are in our mid-thirties (don’t want to wait). However I’m not sure how my sister will take it. I would never want for her to thinking we are trying to overshadow her, bc we are over the moon excited for our new niece to arrive. But this would probably make the most sense for our family.

And lastly are we out of our minds? Any advice?