Am I being unreasonable?

I am due in 6 weeks. My SIL is due in 4. We had our in laws to stay at the weekend. And my MIL mentioned she will be having my soon to be niece once a week when my SIL goes back to work.

No offer has been made to us, my husband is quite upset that his mum is favouring his sister other grandchild. I think if you are going to offer to one then you should offer to both.

His brother has already had two children and my MIL looked after them both until they started school. So it really feels as though we are being treated differently... has anyone else had a similar situation. Is it unfair of me to feel like this?

Thanks