I have one 40 gallon water heater servicing men and women restrooms with:

Men’s restroom:
• 2- tank top water closets
• 1- urinal
• 1-lavatory

Women’s restroom:

• 3-water closets
• 1-lavatory

Pastor’s restroom:

• 1- tank top water closet
• 1- shower
• 1-lavatory

I added a new restroom; for instance do I need another 40 gallon water heater?
The new men and women restroom have the same amount of fixtures.
.

You already have what you need in a 40 gallon tank. Restrooms use very little hot water, none in toilets and urinals and limited at the sink. The shower can easily be supported by one 40 gallon heater.

Bob's correct! As it stands you have a 40 gallon heater servicing only 5 fixture units.
Even with the new restrooms it only kicks it up to 7 fixture units. You're going to be just fine. Good luck, Tom

Just to agree with previous posts: You are just fine with one, 40gln heater.