Mom Guilt (Stay at Home)

How does one balance two children under two? I feel insane mom guilt whenever I am holding our newborn so I try to put her in the swing and hold my 18 month old for her naps. I feel like I'm not giving either child enough attention but I'm doing the best I can. My fiancé works a very time consuming job where he is gone from 6am until around 4pm so it is just me home with the kiddos all day.