I think it is pretty unlikely DD2, who has not been vaxxed for MMR (correct?) will shows titres to it as mealses, mumps and rubella are pretty rare, so I would just vax for it if you have decided she need MMR.
Likewise, I would not bother with a titre test for DD1, either, for MMR. She has had 1 shot - correct? One shot is supposed to "catch" 95% percent of the population. The math is on your side that she is one of the 95%.
Chicken pox is different. Figure out how effective one shot of varicella is. It might be pretty high, in which case no titres or shot needed, IMHO.
Lots of people get chicken pox without even knowing it. (1/7, IIRC).
I would do titres on a child I was considerring a chicken pox vaccine for, if they were unvaxxed, never had the disease or if the effectiveness of one shot was low. I would not bother with a CP vaccine period, but putting on my more moderate hat - I would not bother with a CP vaccine until around 12 or so. It is pretty darn mild in the vast majority of school age children and immunity acquired from the wild virus is more likely to last well into adulthood than vaccine acquired immunity.
There is a battle of two wolves inside us. One is good and the other is evil. The wolf that wins is the one you feed.
Book and herb loving mama to 2 teens and one young adult.