Tenses in sentences with more than two verbs

The number of verbs in a sentence is irrelevant. You simply need to decide for each verb which 'tense' conveys your intended meaning. This tense may or may not be the same as the tense used for the previous verb.

In sentence 2 the verb construction is the same (would [not] + infinitive) because you are saying what you would and would not do if you thought there was an intruder in your house.

In sentence 1 you start with the future perfect continuous to express how long your training will have lasted by the start of next month. You then go on to say what you nevertheless do not think you will be able to do at that point in time: I don't think I will be able to dive (simple future). The tense of the previous verb is irrelevant.

As Lewis points out in The English Verb: An Exploration of Structure and Meaning (p148):

It is the verb phrase not the sentence which is the fundamental unit requiring analysis.