how old are your girls? Any way to borrow some stuff? Get hand me downs from friends/relatives living in colder weather?
I got a down coat for dd1 that was ~30and it wore very well at Costco. She wore it for 3 yrs and dd2 wore it for 3 years. For 1 time use, I would get some fleece gloves, hat & scarf and call it good. Wool would be bulkier and more expensive. If you think your feet will be cold, fleece socks are great but again, I dont have any for my kids and we still play outside in <0 weather.
For winter wear that is bulky, I like to travel with those 'space' bags they have some that you can roll to get the air out rather than needing a vacuum.