Feed them on a schedule, twice a day.
Maybe not while they are still kittens, assuming that they are this year's. Kittens need an awful lot of food compared to their size, and I gather that 4-5 times a day initially gradually reducing the number of feeds down to 2 when they get to be 6-8 months old.
Get them insured right away, and registered with a decent local vet - remember that they will most likely not have completed their immunisations yet, will need neutering at about 4 months, and will need to be chipped (legal requirement now). Your vet may do a "kitten" package that covers all this at a slight discount, but if you intend for them to be indoors only then the monthly "flea & worm" package shouldn't be necessary.
Find out from the rescue/breeder which food and litter they are using and don't change that until they've had a chance to settle in. When you do change, do that very slowly over a few weeks.
Read up on the subject as much as you can before they come home especially from organisations like Cats Protection.
And remember - you don't "own" cats, they own you!