Do the aforementioned sucklings establish kinship, and if so, is the single suckling, in the absence of marriage, to be taken into consideration?

We have previously issued a fatwa that this suckling does not establish mahramiyyah (prohibition of marriage) due to the incomplete number of witnesses among those who deem a small amount of milk to establish prohibition, and due to the absence of what establishes suckling-based prohibition among those who accept the testimony of a single woman.

What you mentioned in your question indicates doubt in your previous information, which means that the mahramiyyah is more likely to be non-existent. And the saying of some shaykhs about avoiding disagreement and abstaining from marriage is a matter of piety, as stated in Al-Kharashi's commentary and in Ibn Taymiyyah's Al-Fatawa Al-Kubra regarding avoiding doubtful matters.

Purity is required in cases of doubt regarding suckling, and prohibitory suckling is not established except by five full sucklings, according to the preponderant and fatwa-given opinion, which is the madhhab of the Shafi'is and apparent from the madhhab of the Hanbalis.