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OK, I think I figured out what you're asking. But first I want to share the proper way to describe visual and split in birds (well, as I learned it in cage birds...but the idea is the same with chickens...or at least, it SHOULD be). What you do is put what you SEE first, then the word SPLIT, then the things the bird carries but doesn't show. Sometimes the word SPLIT is substituted with a "/" but it's used the same. So here's how (the way I learned it) your question would be rephrased:
Splash split Lavender X Blue split Lavender
You would get 1/4 of the offspring being Lavender visually, and of that 1/4, half would be Blue and half would be Splash. Thus you'd get 1/8 Blue Lavender and 1/8 Splash Lavender. That's what they'd be genetically. What they'd look like, and how you'd tell a Blue Lavender from a Blue split Lavender (or a Splash Lavender from a Splash split Lavender) I have NO idea.
The remaining 3/4 of the birds would be a mix of Blue or Splash (in equal probabilities), and they'd be either split Lavender or not carry Lavender at all (2/3 probability being split Lavender, 1/3 probability not carrying Lavender at all). You won't be able to tell just by looking which are splits and which aren't.
In genetics, it's sometimes easier to determine percentages involving multiple traits independently first, rather than making a big huge Punnet square. For example, let's separate the Splash and Blue from the Lavender.
Splash X Blue = 50% Splash, 50% Blue
Black split Lavender X Black split Lavender = 25% Black, 50% Black split Lavender, 25% Lavender
To figure out the probability of two things happening simultaneously, you multiply the probabilities of each. So let's say you wanted to know the probability of getting a Blue Lavender. Blue is 50%, and Lavender is 25%. Multiply that together and you get 12.5% (or 1/8).
Like I said before, this is the probability information for genotypes from this cross. How you'll tell a Blue from a Blue Lavender I don't know (especially since Blue varies in depth of color anyway). This is why people frown upon combining Blue or Splash with Lavender -- not because you'll kill a chicken or something, but because you'll have a hard time knowing what you have just by looking at it. And that flies in the face of the point behind controlled breeding.
If you try it anyway, keep the birds for yourself and avoid confusion by not selling to another person unless you explain the genetic background of the breeding. Good luck.
~Chris
ETA
I just noticed that you mentioned two hens, the second being Splash split Lavender. So everything I mentioned above applied ONLY to the pair I mentioned above. For the pairing with the second hen, this is what happens:
Splash split Lavender X Splash split Lavender = 25% Splash, 50% Splash split Lavender, 25% Splash Lavender
If you are keeping eggs from each hen separate, that's the probabilities for each. If you're pooling them together, the math gets more complex. This is because you'd have to know how many eggs came from each hen, how many actually hatch, etc. If one hen has twice as many hatched offspring as the other, then for the whole group, that hen will have 2/3 of the offspring, so her probabilities would also account for 2/3 of the whole group. If both hens had an equal number of offspring, then you'd have to multiply the percentages for each hen by 1/2, and add together probabilities for like-genotypes from each to determine the probability for the group. So if Hen A has 1/8 Splash Lavender and Hen B has 1/4 Splash Lavender, you'd do this: A + B = (1/8 X 1/2) + (1/4 X 1/2) = 3/16 Splash Lavender. Again, that's only if each hen has the same number of offspring (multiplying by 1/2 means that each hen's offspring are 1/2 of the total....if one hen has 1/3 and the other 2/3 then you use those fractions...etc.).
I think I've already made it too difficult in trying to sort this out for you based on odds....especially considering you'll probably have to post pics here on the forum and ask people to help you determine which are Splash Lavender and which are Splash, and which are Blue Lavender and which are Blue. And when that happens, I can't help you at all.