Question sur l'agence des frontières au royaume-Unis

Bonjour,

je poste ce message car je suis actuellement en contact avec une famille de Londres pour être au pair, que j'ai trouvé via un site d'annonces, cette famille me paraît fiable, elle me propose de m'envoyer un contrat d'au pair, elle m'a également parlé de l'office britannique des frontières pour pouvoir m'employer en bonne et dûe forme, voici son message:

We have decided to find an Au pair because we need help looking after
our child. We are looking for an Au pair to be a big sister or brother
to our child. Our family has decided to disable our profile on
aupairplacement.com since we found your profile and wish to stop
communication with intending Au pairs.

We shall be undertaking the costs of your Flight Ticket and travel
documents. Accommodation and feeding shall be provided by us. All
these details and other information about our contract offer shall be
sent to you in the approved contract letter once we receive it from
the Home Office Authorities. Would like your necessary travel
requirement procured soon.

I have filled the necessary inquiries on how to go about employing you
from the UK Home Office here and I shall be sending you the
information once I have received it, hence wait for update and travel
guidance/instructions so that you do not make any mistake.

we have to have a contract agreement before any other thing so i
advice you wait after sending the contract to you so you can sign and
send a copy of it to the UK Border Agency OK.

Also i need you to send down your resume so that i can prepare our contract.

j'avoue que je ne comprends pas de quoi ils parlent et ce qu'ils entendent par l'agence des frontières