What is the tone for "yi" in these sentences?

It is the sandi of "一”
Usually, “一” ’s tone is 1st tone (yī).
1、When the character following "一 (yī)" is in the fourth tone, the tone of "一" changes. It changes from the first tone to the second tone. However, when writing its pinyin, it is still written as 1st tone "yī".
eg: 一定 →read： yí dìng
written：yī dìng

2、When “一” is followed by a first, second, or third tone, it changes to the fourth tone (yì).
eg：一起→read： yì qǐ
written：yī qǐ

This is a tone change, not a polyphonic character. Therefore, not all reading materials will mark the changed tone.

应该是轻声吧。lā yi lā, niē yi niē

I think should be light tone.

Even if there is some tone in theory, it is pronounced so lightly and quickly that it essentially comes off as a neutral tone.

In these children’s rhymes, the pattern “Verb 一 Verb” (e.g., 拉一拉, 捏一捏) is a rhythmic reduplication. The “一” here is a filler syllable with no lexical meaning. In spoken Mandarin such a filler is normally reduced to the neutral tone (toneless, unstressed “yi”).
So we say:
耳朵耳朵，拉一拉 → lā yi lā
鼻子鼻子，捏一捏 → niē yi niē
Neither the 1st tone yī nor the 4th tone yì is used; the syllable is simply unstressed. The tone-change rule for 一 only applies when it carries the meaning “one.”

Normally, “一” is pronounced with the first tone (yī).

But when “一” is followed by a fourth tone, it changes to the second tone (yí).

Example: 一定 → yí dìng

When “一” is followed by a first, second, or third tone, it changes to the fourth tone (yì).

Examples:

一天 → yì tiān (first tone after it)

一年 → yì nián (second tone after it)

一起 → yì qǐ (third tone after it)

BUT if “一” is used as a numeral in counting or on its own, it stays first tone (yī).

Example: 一，二，三 → yī, èr, sān

i think we use the second tones, because already have a rule in HSK 1 when we can use the first tone and when we use the second and the fourth tone

The pinyin of Google translate is not correct, but their pronunciation is correct, so you can click the volume button to hear how they spell it. You should always pronounce it with the 4th tone based on the rule. As you can see, if you pronounce three syllables with first tone next to each other, it is really hard to pronounce them correctly, and 1st tone + 4th tone + 1th tone combination is also more pleasant to the ear