toddler/booster seat

my husband has family coming down in June and they need a carseat for both their kids. one is 5 (maybe 6) and the other is 2(or 3) anyways so i was thinking i would get a 3 in 1 seat that the older kid could use and then afterwards keep it for myself as an extra carseat and then a booster down the road since lilly will be in her MA for awhile. what seat should i get. i swear all the good seats are in the usa. we don't have seats that harness past 48 lbs even though they are the same seats as usa. i am keeping lilly in her MA until 65 lbs. (apparently they are trying to change the laws in regards to harnessing longer) anyways... lol any recommendations. thank you>

[QuassEE]

You'll need to post their weights, heights, and torso (seated) heights before anyone can hazard a guess. Chances are that the 5-6 year old might not fit in any harnessed seat available, and may be in a backless booster at home they can just bring along and you'll only have to worry about a seat for the 2-3 year old.. in which case a combination you can use later might work great.. But again, we'd need to know how big they are.

-N.