Yes... do it one at a time... you likely will have to re align the motor to the shaft... Usually you release the bolts of the transmission
to the prop shaft.. and re attach and align the plates of the coupling by raising or lowering the engine
mounts or even moving them laterally. You align the engine to the prop shaft. Once all mounts are installed the plates must be perfectly parallel for alignment. When the are parallel.. torque the coupling bolts... and the engine mount vertical alignment nuts.
Re-torque all the nuts. Engine should run without vibration nor water
from the shaft coupling or stuffing box.
Basically it goes something like this if there is no sail drive:
all the mounts you will be replacing. Verify that they are identical... and match the hole pattern.
Remove engine parts
to gain access to the bolts and the engine brackets which the mounts are connected to.
Before removing ANYTHING take pics
Put wood blocking under the engine at the location of the mount you are replacing. Large footprint is better.
Remove the top nut on vertical adjustment bolt of the engine mount.
Measure the height and lateral location of the engine before removing the BRACKET to ENGINE BOLTS.
Loosen the bolts securing the bracket to the engine.
the bracket off. Clean removed parts
Remove the old engine mount - clean or paint
the stringer as needed.
NOTE: you want to put the new mount as close to where the old one was in 3 axes if you can.
Bolt the NEW engine mount to Stringer.
Raise or lower bolt to the height of the bolt of the removed mount. You want the same height. If the mount has slotted holes for the bolts you use this for lateral (athwartship) alignment. Before torquing the mount to the stringer... bolt the bracket to the engine and position the engine mount so the vertical alignment bolt goes straight through the bracket when the bracket bolts are torqued down tight.
USE a PIPE to extend the wrench for leverage (torque). Once the bracket it torqued down AND the mount is aligned and the vertical alignment bolt plumb, and the lower bolt is raised right up to the bracket.... torque the bolts/nuts to the stringer.
Put the top nuts on the engine mount vertical alignment bolt. hand tighten. At this point all nuts are torqued except the top top nut of the vertical alignment bolt.
REPEAT the above for each mount.
Align the engine to the shaft by raising or lowering the engine mount nuts. When the coupling plates are parallel torque the bolts on the plate and then all the engine bracket and engine mount bolts.
Put all the parts back on the motor... belts etc...