Currently. For a Vampire PC to bite another PC we have two options.
We can use the toggle "Vampire Bite" which on your next successful melee hit will bite them. This is great, unless you are an Archer or a Mage and you do not have the Melee AB to actually bite most things. Even things you have immobilised are difficult to bite.
It is even worse to use against players, because you have to hit them to succeed. This often escalates anything into PvP.
For RP Interactions we have the commands that few player know exist. So you must spend a small period of time explaining how '-thrall offer' works in tells and it can be quite confusing. Then you can utilise the -feed command to have a purely thematic bite. This makes things extremely lumpy and OOC.
My suggestions is to have a Vampire Bite toggle a targeter that when used against a Non-Hostile PC will open a window the the following information.
"Character Name is attempting to bite and feed from you. This wll incur a -2 CON penalty for a short period of time. It does not damage your Character"
"Allow"
"Resist"Allowing will permit the bite to happen. Resist will notify the Vampire that they are resisting. At that point, you can choose to how to proceed with the interaction.
The second part of my suggestion is to include an addition to the way in which the current "Vampire Bite" functions.
If the creature is Stunned. Dazed. Prone etc. Then the Vampire Bite automatically succeeds. Similiar to how a Coud De Grace will hit a sleeping NPC regardless of the AB you roll.
This means that in combat, it is unchanged. You need to successfully hit your opponent to bite them. But it also allows users with no Melee AB to have the ability to forcefully bite immobilised creatures