Petunias and Delphiniums need cool nights (below 21 deg. C) to germinate, so you are going to have problems if you cant give them those temperatures. Salvia depends on the species: S. coccinea and S. farinacea need warm nights, while S. splendens and S. hormineum need cool nights. Other species have other requirements.

Forget the delphiniums. They require cold winters. The substitute is larkspur. I sow it outside in the autumn and it grows all winter then flowers in the spring & early summer. But it is an annual.

You may be able to give them a good cold treatment starting in damp paper towel in an open plastic bag in the refrigerator. (you could use any damp material that keeps contact with the seeds and any container that can be left cracked to breathe a little) Keep damp until you see sprouts. That sounds like the cool they might need, then you can plant them. Petunia will do a nice show but delphinium will only do the one summer. Potted you may be able to give them a cold treatment placing the whole pot in the refrigerator for a month or so in winter, but that would be a lot of space and a lot of process. Good luck!

Thank you all for responding to my question. I will try again to do it.