I think it's easier not to combine when dc are around 3 years apart, as mine are, but that could be just me. What I've found is as the older child grows into more independence, my teaching time with that child goes down. About that time, my next child's teaching time begins going up, which is perfect, because that's about when that child really needs me. In contrast, my older child is ready (and wanting) be more independent and do things without me then. I see this rise and fall cycle coming with my third child too. About the time my teaching time goes up with him, my middle ds will be needing me less and less, and my oldest will be near to total independence. However, you can combine with 2 1/2 years apart too, you just have to be willing to wait for little pumpkin so he's not stretched too far always. So, it really is a personal preference. Here are 2 options I'd thought of...
Option 1 - combined:
2010-2011: wait, read to 4 1/2 yo, get some learning games, etc.
2011-2012: 5 1/2 yo and 3 yo do LHTH half-speed
2012-2013: 6 1/2 yo and 4 yo do LHTH half-speed, add in right side of LHFHG for 6 1/2 yo - phonics, fine motor skills, math
2013-2014: 7 1/2 yo and 5 yo do LHFHG, 5 yo does it as is, and 7 1/2 yo does right side of Beyond for LA and math
2014-2015: 8 1/2 yo and 6 yo do Beyond, 6 yo does it as is, and 8 1/2 yo does right side of Bigger for LA and math
...continuing this pattern
Option 2 - not combined:
2010-2011: 4 1/2 yo does LHTH
2011-2012: 5 1/2 yo does LHFHG
2012-2013: 6 1/2 yo does Beyond, 4 yo starts LHTH
2013-2014: 7 1/2 yo does Bigger, 5 yo does LHFHG, half-speed?
...continuing this pattern
*Still another option would be to wait to start LHTH until 2013-2014 with then 5 yo. Or, start LHTH 2012-2013 half-speed with then 4 yo. Or, do LHFHG half-speed with younger etc.
If I did combine, I would want my youngest not to be too young the whole way through the guides, so it would be worth it to me to wait for the younger to be old enough. I may start LA and math with older earlier, but I'd wait until the younger was in the target age range of the guides. Option 2 just has a lot more options within it. I think of Bigger Hearts as a crucial year, with training of how to take on more independence. For this reason, and because of the target ages of the guide, it is a bigger teaching year. So, about when your child got to PHFHG he/she would be more independent, and your younger would be getting to LHFHG or so (if you did something half-speed), and that would be so nice. I'd love to hear your thoughts on all this after you've had a chance to ponder it. There are lots of options here, and somewhere within those options is the right one for you and your dc.
In Christ,
Julie