I think in your situation using spacing to show groups would help understand the relation between elements. You could also add the functionality to drag elements around from a group to another and a remove button (this handlers could be placed on the left of each element permanent on touch devices or only on hover for mouse ones).
To give you some arguments:
There is this thing that a users thumb is often only half the size of their phones screen. Depending on the way they hold it, it can be hard to reach the top navigation.
For that reason your solution will be better.
A popular way of hiding a lot of links to a lot of different pages is the drawer menu, hamburger menu or off ...
This is purely a matter of visual cognition - if the visual design makes it easy to group related elements, there is no problem putting anything anywhere, including buttons on a tab space. So long users can interpret the tabs as tabs and buttons (or other elements) as such, there shouldn't be a problem.
In the top example, the distinction is fairly clear - ...
As you said:
But this is against Apple UX Guidelines of using UITabBarController, as there should be just one TabBarController throughout the App.
Therefore bottom tabbar is out since you already have a main tabbar.
Since I don't have the full back story, I'm assuming Timeline, Plans, Conservation and Budgets are the page sub-links.
Here are some ...
Show it at the top.
In my experience on ecomm product grids, users are more likely to visit subsequent pages if you tell them up front that they exist. It gives them awareness of the number of available options. It also allows them to jump ahead quickly if they already know the first pages doesn't have what they're after.
Granular control when necessary
I would have the Create button, near the top of the page (perhaps in a fixed/sticky bar, so always visible) as you mention.
Then if your design is a table of items which can each be read, updated or deleted. Have a column to the far right, with buttons for each action arranged horizontally. These could be simple text links, buttons or icons.