I am sad to hear homeschooling is illegal in Spain, and I have prayed for you.

It sounds like from what you've shared, your 8 1/2 and 10 yo will be well placed in PHFHG, and your 4 yo will be well placed in LHTH.

I still am not sure about the 7 yo, as it sounds like he may fit into the placement chart for the reading portion, but not for the writing portions of PHFHG. I am not sure when he will turn 8 yo either. I started Bigger Hearts with my advanced reader when he was 7 yo and had to slow it down to half-speed for him due to all of the other important skills in it that were important for him not to miss as he needed to grow into the writing they required. After 6 months or so half-speed, he flourished with Bigger Hearts. I personally would have your 7 yo do Beyond Little Hearts for His Glory, or "Bigger Hearts for His Glory" and possibly at half-speed for Bigger Hearts. We've found this easier to do than to tweak an older program for a younger. Or, I'd combine all 3 of them in "Bigger Hearts for His Glory", and use the extensions for your 10 yo. These series of questions Carrie, the author of HOD, posted may be helpful to read through, so you can see why I am giving the placement advice I am here...
viewtopic.php?f=6&t=9344
So, if you were going to combine your 7, 8 1/2, and 10 yo dc, "Bigger Hearts for His Glory" with the extensions for your 10 yo would probably be a good placement, and your 4 yo would enjoy LHTH.
If you were going to have your 8 1/2 and 10 yo dc do PHFHG, then your 7 yo could do either Beyond Little Hearts, or Bigger Hearts (possibly half-speed), and your 4 yo would still enjoy LHTH.
Or you could have your 7 and 8 1/2 yo do Bigger Hearts for His Glory, and your 10 yo do either PHFHG or CTC, depending on where that child fell independently according to the placement chart. If your 10 yo is ready for it, CTC is an excellent program that lets older dc soar with more independent learning. And your 4 yo would still enjoy LHTH!
Or if your 7 yo will soon be 8 yo and his writing is something he will quickly pick up, you could try all 3 in PHFHG and always have your 7 yo drop down to Beyond or Bigger Hearts if PHFHG is too much. I am cautious to suggest this though, as I think the 7 yo will be in over his head and missing many important skills he needs that he would have learned so well and so easily by doing a younger guide, and what's more, is he will continue to be pushed too far year after year, as the guides just get harder. Maybe take a peek at the PHFHG plans, and see if ds can do the "I" boxes independently - the reading, the writing, and the following of the directions in them.
http://www.heartofdakota.com/pdf/PHFHG-sample-week.pdf
This link may help as you consider what is best for your 7 yo too:
Amount of writing in Bigger vs. PHFHG:
viewtopic.php?f=6&t=3602
Any of the above options would probably be good options to consider, but you will know what best fits your family, and whatever HOD guides your family uses, I think you will enjoy them so much! I just completed a year where we did 3 guides with our 3 very different sons (different in ages, abilities, and personalities too!), and had such an amazing year. I know you will love HOD too!

I hope something here can help!
In Christ,
Julie