We can probably clean the flow up a bit, instead of running 3 approvals, do just 1 and pick to either wait for all the approvals or just 1 of them. That way you dont have to do the same steps 3 times.
Then just put the approver field to whats written below but switch to your columns, this way your send approval wont fail if one of them is empty.
Approver1;Approver2;Approver3