Dovevo andare in spiaggia, ma alla fine sono rimasto a casa.

I was supposed ... to go… to the beach, but in the end I stayed at home 

Quando ero piccolo non dovevo portare giochi a scuola.

When I was little I didn’t have to couldn’t bring / I wasn’t allowed to bring… toys to school 

Non dovevo indossare l’uniforme se non volevo.

I didn’t have to wear the uniform if I didn’t want to.

Dovevo andare a scuola alle 8.

I had to / I was required to… go to school at 8.

Sono potuto entrare solo alle 8

I was able to could come go / get in only at 8 (I could get in = potevo entrare )

Dovevo venire con la giacca al matrimonio?

Did I have / Was I supposed … to wear a the jacket at the wedding? (the jacket solo se si intende una giacca in particolare)

Dovevo venire alle 8?

(Did I have) / Was I supposed … to come at 8?

Non ha potuto andare all’università perché non ha superato gli esami.

He couldn’t / wasn’t able to… go to the university because he didn’t pass his exams. / failed HIS exams (a seconda del contesto si può usare anche il present perfect: he hasn't been able)

Non poteva sentire il profumo dei fiori perché era raffreddata.

She couldn’t smell the flowers because she was had a cold. (was cold = aveva freddo; cough = tosse; the flowers solo se sono dei fiori in particolare) 

Potevo stare fuori fino alle dieci quando avevo sedici anni

I was allowed to / could stay out until 10 when I was sixteen ( si può usare anche could perchè è uno stato o azione ripetuta)