Yeah giving 1d6 sneak attack per 2 levels AND extra attack seems might be too much.
I sent a text to the group and a gestalt set of noncasters mixed with non gestalt casters may be the middle ground but they want to do a short playtest before a full campaign.
in my worlds for a while I have allowed for 2 subclasses (warlock only gets 2 pact or 2 patreons not both) but only for 1 class. (so a fighter/wizard can be an eldrich knight and battle master and warmage, or can be an eldrich knight and warmage and spell singer, but not 2 subclasses for both) so allowing both to get 1 subclass instead on a gestalt is something we are talking about.
We also are talking about making the casters take the 2014 backgrounds but letting the non casters take the new playtest ones.