Its been a couple of years, but you just write ;
“we would like to inform you of the bris of our son, which will IYH take place ……….”
There is an inyan to not use the word “invite” rather you are just informing people
I think it would be more grammatical to say:
Brov Todah L’Hashem Yisbarach, Nolad lanu ben B’shaa tova, Habris Tiskayem Bezras Hashem Yisboruch Byom — , — Nissan, etc.
Or,
you can use some form of “Nachnis as beneinu hanolad lanu l’briso shel avraham avinu IY”H”..” instead of just saying the bris will be such and such.