One of the toilets is on a floor above the other toilet. The connection would be about two feet from the lower toilet. Thanks!

Yes, as long as both toilets are properly vented. In my area, you can have up to three toilets on a horizontal three inch drain.

Are these back to back bathrooms?
How will these toilets be vented? Back to you, Tom

Tom, think you missed the part about "floor above the other toilet"
S I did Bob! Thanks for picking up on it.

Depends on code where you are located, but Ohio code you can put 3 toilets on vertical 3" stack as long as they are properly vented. same as mygirlsdad77 except he is talking about a horizontal branch. If they are on two different floors above and below each other lower toilet must be vented indivdually and the higher toilet if it is the top fixture opening on stack can be vented by the 3" stack. Lower tolet can be back vented into 3" stack 6" above flood level rim of top fixture. If you furnish a diagram of what you are trying to do I am sure someone can give you the proper waste and vent layout.

Thanks pros! Glad I asked. Not so good at drawing but I'm adding a 3rd floor bathroom and connecting the drain to a second floor existing bathroom. Don't know where the second floor vent is but I'll guess they used the vanity vent for the shower and toilet which are all about three feet from each other. The order of flow would be toilet, shower, vanity, out. The 3rd floor connection would be between the 2nd floor toilet and shower. If I vent the 3rd floor toilet I'll be okay right? I was concerned the 2nd floor toilet might back up if both toilets were flushed at the same time.

? I was concerned the 2nd floor toilet might back up if both toilets were flushed at the same time. Not to worry. The flushes will be just
The 3rd floor connection would be between the 2nd floor toilet and shower.
That works for me. I take it wet vents ,(see image) are allowed in your area. Good luck, n Tom

? I was concerned the 2nd floor toilet might back up if both toilets were flushed at the same time. Not to worry. The flushes will be just
The 3rd floor connection would be between the 2nd floor toilet and shower.
That works for me. I take it wet vents ,(see image) are allowed in your area. Good luck, n Tom