Questions about gear

We are planning to walk the OT in December and are considering purchasing Gondwana Colo and Jenolan jackets. They have good length. They are reduced in a winter sale. Does anybody have any experience using these??? As a family of 4 - mum, dad and 2 girls aged 13 and 15 - we are also wondering what size packs. The girls have deuter 50 + 10 SL pack each. Should I have a 60 + 10 and my husband a 75 +10??? What type of rain pants do you suggest? Cost is an issue. We walked it 20 years ago and although we hired goretex pants we never used them as it didn't rain. Will our -5 sleeping bags be enough or should we invest in some thermal liners for the sleeping bags?? 
