DNA TEST RESULTS

I have a 2 y/o son and 1 y/o daughter

Fast fwd: I was having entanglements with two guys around the same time.. my sons dad and my ex and I thought she was my ex’s but I’m not certain anymore being the time was so close… neither of them are in my kids life and I’ve been raising them alone but I want to know for sure, and hold him accountable. has anyone done a siblings test before are they accurate?