Eastend - I'm so pleased everything was OK in the end. The babies seem to like to put on a performance for monitors don't they?! Tough situation with the family. I think you are definitely right to think about having space and doing what's best for the three of you.
biking - good luck with the sale completion!
Grubby - your mum sounds amazing!!
jellybelly - that's a really tough situation, and not on for people to presume anything without asking first.
MollieRos - if it's easy for the PILs to make arrangements at short notice then I'd probably ask them to wait until you let them know you're ready. You don't know exactly when your baby will be born and for how long you'll be in hospital or how you'll feel when the time comes. Don't worry about feeling like a crazy first time mum! It's the only time in your life that you'll be one so go with what feels right for you :)
My experience was slightly different because I needed help, I had a c-section and a 10lb baby I couldn't lift easily and DP had just started a new job so had only 2 days pat leave. My mum came down to stay as DP's leave ended and stayed for about 2 weeks. I felt ready for general friends and family short visits from about week 1. I am close to my mum but she lives about 2 hours away so it was lovely having her down. She offered to look after the baby while DP and I went for a meal on day 2 which was amazing (the restaurant was pretty much around the corner so I could run back quickly if needed).
I think the biggest help was having someone to take care of the chores like washing, cooking and hoovering. If they are only prepared to help with baby - specific things, this can make it stressful.
Also, politely encourage visitors to bring tasty food with them 