Usually yes, unless the other funds already reach the full qualifying amount. The capital must be invested or actively in the process of being invested at filing, and a source-of-funds file that depends on payments not yet received invites a request for evidence or a denial.
File when the money is in hand and traced
The petition is judged on the capital actually committed and its documented source at the time of filing. Hypothetical example: a retired Shannon engineer's buy-back is paid in three annual instalments and his inheritance has already been distributed; if the inheritance plus the instalments received so far reach the qualifying amount, he can invest and file now, documenting only those funds, and the remaining instalments are irrelevant to the case. If they do not, waiting for the final instalment is safer than filing on a promise.
Once filed, Form I-526 or I-526E takes an extended period to adjudicate; residence is then granted when the Visa Bulletin shows availability, and the family enters conditional residence for two years, filing Form I-829 in the final ninety days. A son approaching 21 should have his Child Status Protection Act position calculated before the filing date is chosen, because the petition's pending time is what protects his age. Capital must remain at risk throughout.