Decorate the gym with lots of "girlie" things or you could decorate with a SPA motif (bamboo, rocks, water fountains). Let each sister pic which station they want to start at then rotate through whichever they want.
Station ideas:
Nails(Manicure/Pedicure)
Waxing
Massage (see below)
Make-up tips or tricks
Skin Care
Hair Care
For Refreshments you could serve veggie trays, chocolate goodnesses (you could do a chocolate fountain and set out strawberries, raspberries, pretzel,etc), fruit trays, flavored sparkling water (Wal-mart). Pick foods that really would spoil yourself and the sisters.
For the massage if you live in the northern part of Utah, United States (probably no further than Salt Lake), my sister is a massage therapist and would be willing to teach how to do hand massages or facial massages. Email me if that interests you and I'll talk with her and get back with you.
Here's a handout for you to invite the sisters.
DOWNLOAD 5X7 HERE
OR A SHEET OF 4 (SET PRINTER MARGINS TO ZERO)
