Dog sitting with a newborn..

Sister in law wants us to dogsit for her when we will have a newborn that is a few weeks old.

My partner doesn't see a problem with it, but I feel overwhelmed by the thought already.

We have a dog, a big dog. Her dog is a big dog who is the light of her life, who has never met my dog.

Am I being to cautious not wanting the stress of two dogs for 2 weekends in a row when we will have a newborn? I'm a first time mum, so I feel as though a baby on her own is enough to steal all our focus, let alone the dogs on top of that

Thoughts?