Most hen's nights that i've been to the bride-to-be's Mum is there (& Aunties) ...

Guess depends on your relationship with your Mum & MIL ... and if all is ok & IF you would like them to come depending on their personality i wouldn't make them feel pressured in going ... Keep in mind where you are going to celebrate as there is nothing worse than Mum & MIL feeling any older than what they are ... but then maybe they (or especially your Mum) might be so wrapt to celebrate the night (or day) with YOU