Hi,
If you're twins are 4 year old and are over 16kg then they can go straight into a booster seat (group 3). However, if you're Cab has only lap belts then you may have a problem with securely fastnening them in. You also need to consider the injury that can be caused by a lap belt.
Try this company below:
http://www.quickfitsbs.com/modern_vehic ... tbelts.asp
They may have a solution to you're problem. I've never used them before but I hope this helps. I have 2 kids aged 4 and 8 months. I've had to use seat belt extenders to securely fasten in the baby seat properly. Seat belt extenders can be purchased from:
http://www.porscheshop.co.uk/acatalog/P ... Belts.html
I would recommend going to Mothercare for your car seats. If they have a larger branch near you, they often provide a service of try before you buy, just to make sure you can get the seat to fit correctly.
Ben
