Learn Swedish: Vi bjuder in alla grannar. - We are inviting all the neighbours.

Bjuda on its own can mean to offer, to treat, or to invite. Adding the short word in makes it the specific particle verb bjuda in, which strictly means to invite someone to a gathering, party, or event.

Can I put in at the end of the sentence, like we sometimes do with phrasal verbs in English?

No. In Swedish, the verb and its particle (like in here) usually stay strictly together. You cannot split them up with the object, so you must say bjuder in alla grannar rather than bjuder alla grannar in.

The English translation says 'all the neighbours'. Why is grannar in the indefinite form instead of the definite grannarna?

In Swedish, the word alla is almost always followed by a noun in the plural indefinite form, even when we would say 'all the' in English. So alla grannar is the natural and grammatically correct way to say 'all the neighbours'.

Why is it alla and not all or allt?

Alla is the plural form of the word for 'all'. Since grannar (neighbours) is a plural noun, you must use alla to match it. You only use all for singular en-words and allt for singular ett-words.