Yes, Zeus was his father, making any son or daughter of Zeus his sibling.
No, he does not. The gods are in no chronology and can appear any age they like.
The brothers and sisters of Dionysus are the children of Zeus, they included the Olympian gods Ares, Hephaestus, Apollo, as well as Artemis, Athena, and others.
This is not in any of the old myths.
Yes, he is one of the big three hence Zeus and Hades are his brothers, and all the gods are pretty much inter-related somehow.
Hera was the wife of Zeus, but may have had a Kharites/Grace daughter with Dionysus under the name of Kronois "daughter of Kronos".
Athena did have a few half brothers and sisters. there was Ares, Artemis, Apollo, Aphrodite, Hephastus, Dionysus, Hermes and a few other minor gods and goddesses. But she did not have any real brothers or sisters.
Thebans would have worshiped Athena, Dionysus and Zeus more than any others. They possibly would have cults to Hera and Demeter as well.
Yes The Olympian Gods were: Hephaestus, Ares, Apollo, Artemis, Athena and Hermes. He had many, many others (demigods).
Yes. In fact most of them were related in some way
Yes monthu is not the only Egyptian god of war
Athena, the Greek god of wisdom, is related to the other gods. such as Zeus, hades, Poseidon etc.
As much as any other gods do.