"Get on (well, badly, etc)" is perfectly fine. The thing is, certain verbs sit comfortably with a plural subject. If the subject is single, then you add the other person using "with".
eg. They always argue over politics. She always argues with her father over politics.
Did they break up? Did he break up with her?
The same goes for "get on" (and "get along"):
Jack got on well with his uncle Fester.
Jack and (his uncle) Fester got on well.
They got on well.
I'd actually say that, when the subject is plural, the verb is intransitive (reflexive). Adding "with..." just fills in the missing information.