I wasn't aware that Germany had super low income taxes. It is certainly possible to game the welfare system and many people do, but if you want a decent standard of living then you need to be employed.
if you marry you basically half your income tax burden if your partner is not employed. there are also child support payments from the government of several hundred € per month that you get as well as free kindergarten, schooling and higher ed. if you are poor you get money from the state until you hit a minimum income threshhold which together with all the other payments is more than enough to have 2 children.