$12,345 · 2 Toddler carseats legal in Europe

We are heading to Scotland for a 3 week vacation soon, taking our 1 and 3 year old children. Car seat dilemma is real and we are leaning towards buying two new car seats once we land, since rates for renting the two car seats with the car rental agencies are outrageous (more than the car) and anything we can easily purchase here isn't legal there. Anyone heading to Europe in the Fall facing the same issue!? We could bring back the two car seats and sell them at cost. Both would be R129 (circle E) rated for Europe.