Can Sony use Holland's Spider-Man in their spin-off movies after this Marvel deal?
Honestly, I find hard to believe Marvel didn't think about the possibilities after this deal. Back then, based on the leaks or rumours, Sony was planning even an Aunt May movie. So Marvel was well aware that Sony had the ambition of expanding the Spider-Man universe, either with Aunt May, or Sinister Six, Venom, Black Cat, etc...
Holland's Peter Parker was introduced in the MCU. So, by using him in other movies, Sony would be expading the MCU as well. So I believe there was some sort of clause in the deal to avoid the use of Holland's Spidey (Now part of the MCU) in other projects like Venom, Morbius, Kraven, etc... I don't think Marvel didn't consider what could happen after this deal. I think Sony would need Marvel's authorization to use specifically MCU's Parker.
Now, with the success of Venom and the end of this deal, I think this might come as a condition for a new deal: Marvel can continue to use Holland's Spider-Man for a few MCU movies (or even other heroes and villains like Spider-Woman or Green Goblin, for instance) in exchange of using some MCU characters and allowing Holland's Spider-Man to be part of their spin-offs.
Just a thought.