If you find it difficult to play the hymns fluently in 4 parts, one of the easiest techniques is just to perform two outer voices - soprano with the right hand and the bass with the left hand with the loud registration (maybe principal chorus with mixtures).
Each hand takes one part. That will make it super easy for you.
But the beautiful part is this: your congregation almost won't notice anything bad with this because the two outer voices are the most important parts in most pieces, especially hymns.
Soprano is the melody. This makes it very important. The bass is the foundation of harmony which is crucial too.
Actually, you can even imagine the two missing parts by hearing soprano and bass lines.
Just try it and see if you like it.
It's a shortcut for an emergency, if you can't play all 4 parts.
But if you can play hymns in good tempo fluently, then by all means play all of them.
Hope this helps.