MongoDB restoring to existing replica set (avoid creating a new one)
No. Copying to Secondary will not help
Yes. Primary will replicate the data to Secondary. Follow the steps below
Re-creating the replica set is not an option


Steps:


You can restore it on the Secondary node first
Next, Switch your Secondary with restored data to be the new Primary. Now the Primary has latest data
Bring down the Secondary, erase its data and then bring it up (Do a Resync) so it can copy the data from the Primary with latest data
Repeat the same on other Secondary
Once done, you can switch your Primary if required