This question is actually quite complicated because of the uncertainity and lack of evidence. Plutarch is pretty much our only source which mentions Q. Servilius Caepio and it is through such passages that we understand the relationship between M. Cato and Q. Servilius Caepio (Plutarch. Life of Cato Minor. 8.1; Moralia. 16/487c). The interesting passage is in the opening of the life of Cato Minor (1.1):

Cato's family got its first lustre and fame from his great-grandfather Cato (a man whose virtue gained him the greatest reputation and influence among the Romans, as has been written in his Life), but the death of both parents left him an orphan, together with his brother Caepio and his sister Porcia. Cato had also a half-sister, Servilia, the daughter of his mother.

Here, Plutarch refers to Caepio as Cato's brother, yet refers to Servilia as his half-sister. It is understood that Caepio was the half-brother of Cato, with Caepio's father (also. Q. Servilius Caepio) marrying Cato's mother. But, it is pretty certain that they were half-brothers only.

Now, moving onto your questions. It is unlikely that Cato's half-brother is the same Servilius Caepio that was promised to Julia, who is in fact is only referred to in texts as either Caepio or Servilius Caepio (Plutarch. Life of Caesar. 14.7).

In terms of the evidence that Cato's half-brother Caepio married a Hortensia, it is only true if correct that it was this Caepio that adopted M. Junius Brutus. We know that M. Junius Brutus from textual evidence that by 59 BC he was being referred to as Quintus Servilius Caepio Brutus. This suggests that he was adopted by a Servilius Caepio, although which one is debated. Some scholars, such as Treggiari (Servilia and her family. 147), argue that Brutus was adopted by his uncle (his mother Servilia's brother and Cato's half-brother). Other scholars, such as Geiger (The last Servilii Caepiones of the Republic) argues that it could not have been Cato's half-brother that adopted Brutus (he states that Cato's half-brother died with the only heirs being mentioned as his daughter and Cato, and because the textual evidence only refers to Brutus by his adopted name from 59 BC). Geiger offers a solution that Brutus was adopted by a half-brother of Servilia, but such idea does not really have much support from scholars who believe it was Cato's half-brother who adopted Brutus. Eitherway, there is an inscription from Delos (43 BC) that honours Q. Hortensius Hortalus and identifies him as the uncle of Brutus which would suggest that the Caepio who adopted Brutus had married a Hortensia. If one believes that it was the half-brother of Cato who adopted Brutus, then it would be him who would have married a Hortensia.

In terms of the death, Plutarch gives the date of Cato's half-brothers death as being 67 BC (Life of Cato Minor. 11.1-8). The suggestion of that Caepio died in 59 BC stems from the above argument of there being a different Servilius Caepio.

Hope this can shed some light on the situation, as I said it is difficult to provide certainty simply because there is a massive lack of evidence.