I use with my 8 yo dd and 5 yo ds. You can do some together – phonogram and sound review and key card review – as games and whatnot, but I would keep the actual lessons separate unless they are in the same level. If in the same level, they might start together and advance at different rates.
I’m away on vacation w/o my books, but right now ds is on step 1 phonogram learning, we’ve been there a few weeks. We review them for about 10 minutes a day. His favorite is jumping up and down steps when he gets it right. For dd, we work on a step as laid out in the book for about 30 minutes (but she’s used to 1.5 hours from SWR) and stop wherever we are.