Father rights

How can a dad get full custody he isn’t on the birth certificate I left him 2 years ago and he’s probably visited a total of 4 days total if I add up the hours he comes every 2-3 months sometimes longer for 20-30 min and he’s on his phone the whole time we broke up because he had a pill addiction I wasn’t aware of until he confessed to me and he never changed a diaper or feed our 2 kids whenever I would ask he would argue with me he never changed there clothes nothing I left him when our kids where 1 yr 3 months they are 3 years and 4 months now we broke up 2 years ago this coming January it will be 2 yrs and he is always threatening me he’s taking full custody he called cps because he said he right I was talking to someone or dating and cps just dismissed everything the same day after my children where checked by a dr and cleared them I’m afraid of what might happen please help he is paying child support well he has to pay because I asked for cash aid but they said it had to be child support he pays a total of $400 for our 2 children what can I do what are the chances he can get full custody I live in California his sister also did tax fraud saying he gave our kids information to do taxes and even received stimulus checks I did report her not to say when we did break up he was probably more on drugs because of the breakup and our kids got sick once we broke up and I moved with family and they where hospitalized and I text his mom and sister and they ignored me and they told him not to show up cuz he wasn’t a dr and he couldn’t do anything his mom hates our kids and she wants him to never be In there life she’s evil I don’t want my kids around his family what can I do please comment your Tought thanks 😓 I read all your comments thank you so much for the kind words and for the advice I will take it all and I will also talk to an attorney cps did suggest I go and try to get full custody but I haven’t went because I’m afraid they will actually give him time because I know he probably still uses drugs when cps did come here they asked me to drug test and I did and he told me they told him to test and he refused to and he said one of the 3 people from cps laughed and said oh u don’t want to test because u smoke marijuana and u will fail right but he admitted to me he uses cocaine and pills so I don’t get why cps would brush it off I also know he keeps drugs and guns in his home and I know his mom and sister hate me so I don’t want my kids at that house at all it’s been since 2019 since his family saw my children and I want to keep it that way also can I also report be refused to drug test and he did say that cps just brushed it off