Catherine: There will always be gatecrashers.

凯瑟琳：总会有闯入者。

So Catherine is saying if push comes to shove they can buff up their numbers by letting in gatecrashers.

所以凯瑟琳说， 如果到了紧要关头， 他们可以通过让闯入者进来来增加他们的人数。

A " gatecrasher" is a person who goes to a party even though they were not invited;they just go to the party and show up.

“gatecrasher” 是指即使没有被邀请也去参加聚会的人； 他们只是去参加聚会并露面。