The word that seems to throw everyone out is “costestes”, which is not actually a “Classical Latin” word, but is used in Ecclessiastical Latin - a subtle derivative of the Classical language that is historically used in Catholic Churches.
The best translation to English would be:
Silent Witness
The spirits that also bear testimony
(In) silence.
Silent Angel
The spirits that also bear testimony
(In) silence.
A break down:
Testator Silens
{One who bears witness in silence}
Silent Witness
Costestes e spiritu
{Co-witnesses (or those that bear witness alongside other witnesses) from (as in, formed of, or originating from) the spirit}
[Those that are made of the spirit bear witness alongside other witnesses]
The spirits that also bear witness
Silencium
{Silence}
(In) silence.
--
Angeli Silens
{Silent Angel (or Angel of Silence)}
Silent Angel
Costestes e spiritu
{Co-witnesses (or those that bear witness alongside other witnesses) from (as in, formed of, or originating from) the spirit}
[Those that are made of the spirit bear witness alongside other witnesses]
The spirits that also bear witness
Silencium
{Silence}
(In) silence.
Another possible variation of the line "Costestes e spiritu":
Those who also bear witness that are present (only) in spirit