Is it permissible to marry the daughter of the paternal aunt's daughter, knowing that the paternal aunt breastfed the suitor three or four times, but the suckling was not complete, rather it was merely one or two sips?

The preponderant opinion is that prohibition is not established by less than five sucklings. So, if it is confirmed that the suckling did not reach five sucklings or more, then it is permissible for you to marry this girl. As a precautionary measure, you may choose not to marry her, taking into consideration the opinion of those who say that both little and much suckling establish prohibition.