Questions & Answers about Er ist viel sturer geblieben als meine Eltern.
Why is als meine Eltern placed after the past participle geblieben?
This is a classic use of the Nachfeld (the after-field). Normally, the past participle (geblieben) sits at the very end of a perfect tense sentence. However, comparisons starting with als (than) or wie (as) are usually pushed after the final verb so they don't awkwardly break up the main clause.
Why does this sentence use ist instead of hat for the perfect tense?
Even though bleiben (to stay/remain) describes a lack of movement, it is a major exception in German grammar. It always takes sein as its helping verb in the perfect tenses, never haben.
Why do we use viel here instead of sehr for "much more"?
Just like in English, you use viel (much) to emphasize a comparative adjective (sturer). You cannot use sehr (very) with a comparative; you would say sehr stur (very stubborn) but viel sturer (much more stubborn).
Does sturer have an adjective ending here, or is it just the comparative form?
It is just the comparative form. Because the adjective comes after the verb (as a predicate adjective) and doesn't stand directly in front of a noun, it gets no grammatical case ending. The -er is purely to make it comparative.