There are many ways to raise offsprings. One could individualize each specimen in single tube, group together 5 or 10 critters, or even communal rearing can be done.
Concerning the species taking up all the space provided and producing amount of silk (as Latrodectus obscurior for exemple), the cannibalism is naturally reduced by the space between each young while for the species staying in groups in corners with only few silk wires (as Latrodectus tredecimguttatus), the proximity associated to the poor silk playground could lead to a high rate of cannibalism especially when hunting (the hunter become the prey of the neighbour as it agitates to catch the real prey).
I advise to split the “agglutinated” species into smaller groups of few individuals, whereas keeping other species in one collective big tank. According to my observations, single offsprings tend to feed worse than group offsprings, grow slower and come to weaker adults that reproduce worse.
Anyway, a sufficient quantity of food (even in excess), a substancial tank volume and a significant relief setting (increased usable area; cavities provide shelters) are the key to success.
Latrodectus tredecimguttatus (Rossi, 1790), known as the Mediterranean widow, the Malmignatta or the European widow can also be called the thirteen-spots-widow because of the particular patterns found on the dorsal side of the abdomen of many individuals and often used to identify this species.
Actually this widow shows numerous colour variations to such an extend that the varieties have been formerly splited into distinct species [Walckenaer 1837]. Melanic and melanotic ones are often misidentified and other diagnosis tools have to be used.
According to Antonio Melic in his paper on the widows of the Iberian Peninsula, the female’s abdominal bifid setae of this species is a distinctive feature that separate it from other mediterranean and african species. Here are some pics below of the famous bifid setae.