2个人米兰到巴黎夜车，包厢铺位应该如何选择

本人10月3号晚上准备坐thello夜车，从米兰到巴黎。我和妈妈两个人，我们想订一个三人的房间（两人间的价格较贵），主要怕不安全，价格是150欧/人。对以下的铺位不理解，不知如何选择：
Letto in cabina a 3 - Donna
Cabina a 3 - Intera

我想是两个人在一个房间，adult一开始我选的是2，但是我选择Cabina a 3 - Intera（我以为是一个包厢的意思），系统跳出：
Error code: 1234 Complete compartment service can be acquired or modified only if the travelers number is equivalent to the compartment seats number 以及

Full fare
The communicating compartment flag is elegible if the number of travelers is equals the capacity of 2 compartments , The communicating compartment flag is elegible if all travelers of the same compartment select the same option , The communicating compartment flag is elegible for at least 2 travelers, Complete compartment service can be acquired or modified only if the travelers number is equivalent to the compartment seats number。

我理解是选择的人数不对。我们是两个人，请问我该如何让我们选择到一个包厢内呢？