Compare the actual engagement terms. Two matters can involve distinct work, but a shared file review or combined arrangement may avoid some duplication. Ask who will reconcile the case histories, which fees already cover that work and what new charges apply. Neither an investment payment nor an assumed retainer scope settles the professional budget.
Ask for scopes, not a single lump figure
The duplicated work is real: reviewing the earlier record, reconciling dates, and advising on whether to withdraw are billed by someone. Do not assume every cost is paid in one instalment, and do not assume a retainer covers the coordination between the two files unless the engagement letter says so. Ask both firms, in writing, what is inside the fee and what is billed separately.
The duplication becomes visible once you list the tasks by who performs them. Reviewing the earlier record is work for someone; reconciling dates across two files is work for someone; advising on withdrawal is work for someone, and it may be work only the employer's counsel is positioned to do. Ask each firm to state in writing which of those three it is taking on, and whether coordinating with the other firm sits inside its fee or is billed separately.
A retainer signed for the EB-5 matter does not oblige anyone to read a file held elsewhere unless it says so, and the item nobody is engaged to do is the item that will not be done.