Suggested answer:
(1) Practice, focused, and fulfilment are the preferred spellings in the corpus.

(2) According to the corpus header (which you get access to by clicking on the text code at the end of the line in the corpus search result), all forms have been used in both American and British English. Nevertheless, in some cases there appears to be preferences as to which spelling is chosen in the two varieties. The spelling fulfillment is most common in US texts, e.g.
The happiness and fulfillment which are the ultimate consolation of the fairy tale... (Region: US)

This spelling, however, is also recorded in UK texts:
...no particular purpose other than the wasteful fulfillment of its own internal momentum. (Region: UK)

And although fulfilment is most commonly found in UK texts, there are also examples of this spelling in US texts, e.g.
The Factor of Flow is connected with the fulfilment of the action... (Region: UK)
Fulfilment of this historic possibility depends in part on the role... (Region: US)

The same tendency can be seen for the pair focused vs. focussed, with the former the typical spelling in British English and the latter in American English, although both variants have been used in both Bortish and American texts, e.g.
...whereby governmental authority is focussed. (Region: UK)
...before my eyes focussed and I carefully turned my head. (Region: US)
Then his eyes focused. (Region: UK)
The concerns of her luxurious life were now tightly focused. (Region: US)

(3) To some extent the difference in spelling between practice and practise can be attributed to American vs. British spelling. Buth there is also another dimension added to the difference — the spelling could reflect word class, viz. noun vs. verb. In both varieties practice is a noun, e.g.:
This is a pernicious practice which can only lead to... (Region: UK)
Yet one who is unfamiliar with laboratory practice will find... (Region: US).

The corpus results show that the verb is typically spelt practise in British English, e.g.:
...such individuals very seldom practise what they preach...

American English uses practice both as a noun (see example above) and a verb, e.g.:
He had had little occasion to practice the arts of hiding and escape in New York.

This is merely a tendency, since practice has been found as a verb in British English texts and practise as a verb in American texts, e.g.
...I was advised myself to practice the art... (Region: UK)
...we identify a culture with the people who practise it... (Region: US).

What seems to be fairly stable is the use of practise as a verb, although this example shows otherwise:
They said it was a practise run.

Conclusion: The corpus has shown that the word pairs focused on here have preferred spellings in the two varieties of English, although there is not 100% consistency. However, it is advisable for learners to make use of the typical spelling of the variety of English used.

Read about spelling here.