I can see why you are confused. The different dictionaries you chose use different phoneticization systems, so that is the cause of some of the confusion. The "y" in source 2 and the "j"s in sources 1 and 3 actually represent the same sounds: all 3 represent the sound that is written as "y" in English and Pinyin. However, the different sources DO recommend different vowels after the "y" sound. This is because the name is originally Russian, and English doesn't have the precise vowel that Russians use at the beginning of the name. We use different vowels to come close. So, as a Chinese speaker, you can follow 2 different strategies. One is to FULLY anglicize the name, and pronounce it as if it were the English surname "Jacobson", instead of the Russian surname Якобсон. If you choose that option, you should say ˈdʒeɪkəbsən and mimic the "american" pronunciation in the Collins dictionary. Your other option is to listen to these recordings in Russian, and try to mimic the Russian pronunciation: https://forvo.com/word/%D1%80%D0%BE%D0%BC%D0%B0%D0%BD_%D1%8F%D0%BA%D0%BE%D0%B1%D1%81%D0%BE%D0%BD/#ru