My DD1 is 3.5 and DD2 is 4 months, so similar in age to your two. My DH works away a couple of nights a week, and I'm just starting to feel that I'm dealing with bedtime on my own (quite) well. So this is what I do
After tea DD2 gets a BF (one side), so that she's not hungry and screaming for milk. DD1 winds down with a book or CBeebies
I don't try to do too much - bathing both at the same time with only one pair of hands is too much like hard work for me. So I alternate bath night (they survive if they only have a bath every other day), or if they are mucky/sweaty then DD1 gets the bedtime bath and DD2 gets a morning one, once DD1 is at pre school and out of the way.
I get DD1 involved - she chooses DD2s pjs and lays out her nappy. Then DD2 'chooses' DD1s pjs.
DD2 is put in her bouncy chair and we sit on cushions next to her for a story - being close to her seems to keep her quiet as she likes to watch and listen. The one thing DD1 hasn't accepted is DD2 getting cuddles at bedtime, otherwise they get on great. So sitting next to DD2 gives me an arm free to cuddle DD1.
If DD2 is grizzling and we can't hear the story, then I'm afraid to say she goes into her room, in her cot with the mobile on and we close the door. I feel terrible, but actually this way I get DD1 dealt with quicker and get back to DD2 sooner. This was the best piece of advice I got (from an MNetter of course) - if you have to leave one child unattended, then make it one who is the least destructive! A baby will cry, but will forgive you once it gets a cuddle again. What in earth will a toddler get up to?!
DD1 gets a quick cuddle and then I go to feed DD2. If DH is around, then he will stay with DD1, but otherwise she is told we love her and to sleep tight, and she will go to sleep on her own. She is capable of going to sleep on her own, just prefers the cuddle.
When DH is around the 4 of us do the same process together - it takes longer than each of us dealing with one girl, but it is a consistent routine and they've fallen into in happily.
How soon does your DH go away? I'd 'practice' with DS1 going to sleep on his own and also with all of you doing the full routine together, if you have time. It is do-able (and this comes from someone who was very stressed about it 2 months ago), but it often takes 2 hours from start to finish! Make sure you have a cuppa or a glass of wine ready once the house is peaceful and still!