where to instal the password export server in the child domain

i am migrating child domain to parent

in the child domain i have 2 DCs as below

dc1 - infrastructure

dc2- pdc, rid and GC

now i need to install the password export sever on the source domain - child - and the ADMT on the destination - parent

my question is on which DC in the child i should have the password export server & is it recommended @ this stage to consolidate the 2 child dcs into one or after the migration