theoretically they should be fine.  Although things can happen.  but then
again, they can happen when you are at home as well.    If your boys are
needy, Id probably recommend that the sitter stay with them a bit and give
them some attention.  If they aren't, then they should be fine.

Since there are two of them, they will have each other for companionship,
and once a day would probably be alright as long as there is adequate food
and their box(es) are scooped regularly.

We have always had someone come in twice a day, mainly for companionship
(although we also had two cats at the time).  They get both canned and dry
food, so feeding canned twice a day insured its freshness.

When I go out of town I have a "cat sitter" check on my cats twice a
day.   They feed the cats, give them water, give them
some love and attention, play with them, bring in the
mail, turn on some lights, turn off others, let
me know if anything is wrong, and clean the litter box.

The one I use i know is good, she worked for my
vet a number of years ago.

I should mention my cats hate to be left alone.
They hate it with a passion..