These kind of games are plenty exploitable. If they are that nitty, you should be able to squeeze several bb/hour out of them easily. Which is pretty good! That's what you'd hope for in any other game over the long run! But it's not sexy because it's such a slow, smooth line upwards. Maybe you just like gambling.
Early position: limp speculative hands, raise large with value hands, fold marginal hands
Folds to you in late position: raise small with just about everything (literally everything can be okay if they are too tight!) - careful though, huge difference in ranges between btn/co. HJ is not late position.
Limps to you in late position: raise large for value, overlimp speculative hands
Bluff 1/3 to 1/2 pot on all favorable flops. Favorable being anything it is hard for a limp/caller to hit. Flops with two low cards and a non-ace high card are great. Flops like QJ9 are bad.
Usually A-high flops are bad too, because live players like to call raises with Ax so they end up having an enormous amount of aces in their range. But some super nits will call large preflop raises with any pair just to set mine, and not even peel a small flop bet if they miss. So a small cbet on a-high boards can still be profitable even if their range has huge equity. Player/situation dependent.
Turn, called, bluffing: Give up
Turn, called, value: Bet/fold whatever will get called by worse even if it is very obvious and exploitable.
Turn, called, monster value: Bet whatever will get stacks in even if it is an overbet. Bet more if turn is dynamic (meaning hand strength can easily change by river, eg. flush draw, straight draw, highest card is low). Nits have been waiting all day to hit an overpair and aren't going to give it up now.
bonus: So if you're clever you may notice, why are we giving up turn when bluffing but betting small for value? Good question. Barelling nits works too
Either they call wider than you expect and you can valuebet larger, or they do fold pairs and you can bluff. But obviously that's a lot more player dependent and then the strategy becomes a little deeper than following a flowchart. Probably don't triple barrel bluff.