Hi Paul,
to the forum, we'd love to see some photos of all the furries, doggies included
As to your question, as i am sure you know Bengals are very social cats and love lots of attention and friendship alike.
I think that provided you think the other two would be ok with it, another cat or two probably won't mess up the mix. It really does depend on how well you know your cats right now, and the dogs. Do they get jealous easily? Do they fight for your attention? If so another cat or two might annoy them, but if they are the type of cat and dog that aren't overly fussed because they get to play with each other I would think that if you add more it won't be too bad. Bengals will generally socialise with others well, and provided they are spayed/neutered there is no competition so to speak amongst either sex.
Again, we can only give you advice from our own experience, but you really know the habits and personalities of the furries in your care.