advice on set up

hi i want to take some portrait pics of my 3 kids at home .I have 30d nifty fifty 28-135is and 430II also 5in 1 reflector.
I have a space i can use by french doors with nets to allow a soft light through.If i get a backdrop what kind of result can i expect dr i really need to invest in a set of lights ?
have seen interfit advertised for £200 and thats with backdrop + lights +softbox+reflective umberella.
but do i really need to spend that much some pics of what i could expect would be nice.

cheers shane

Portrait photographers got by for many years without lights. Sure it's possible to use the window lights. You may want to get some sort of a reflector to open up the shadows. Simple cheap solutions include large sheets of foam-core, or those auto heat shield things. (The ones designed to put inside the windshield) Then get experimenting. If you had lights in a studio, you'd be in more control, but there's no reason you can't take a good photo with the limitations you list.

EDIT: Oh you've got the 5-in-1... great! Sorry, my bad.