2019 amended return to claim 3 children

Good Morning,

My boyfriend needs to file an amended 2019 tax return and claim 3 children(had an agreement through court and the mother claimed them, we took her to court to get  the 8332 form) I was wondering if he would have to file an amended return for 2020 as well due to stimulus payments? Also how should he file those? This is his year 2021 to claim all three children again, should we file this tax year then the amended return? Thanks!