Probably _chivi_ is a mistranscription of _chwi_ 'you'. Then:

Nos dda y chwi fy Fam [= Mham]. A bendith Dduw fod gyda chwi. Yn cadw chwi bob amser.

Night good the you my Mother. And blessing God be with you. In save you every time.

Good night to (?) you my Mother. And God's blessing be with you. Saving (?) you always.

_Cadw_ = 'Save' is the Welsh national heritage organisation, but I wonder if it's 'remember' here. The verb doesn't have a subject -- _yn cadw_ = '(in) keeping' or something.