1. We know that Beatrice is more like a concept (a title which can be inherited) and that Kinzo was obsessed with Beatrice.
2. We know that "Beatrice" lend the gold to Kinzo.
So my theory is:
1. There are at least three different Beatrice: the one who lend the gold, the one who was living on Rokkenjima and present one (who I think is Jessie or Shannon)
2. Beato (Jessie or Shannon) is not murdering people, the murderer is someone from the family.
3. We have two points of view - Battler sin was leaving the family - that is how Beato sees it, but it was his return that triggered the (potencial) murders, for which Beato resents him (he forced one or more of her family to become potencial future murderer/s). Personal reasons for resentment can also be applied
4. The title of the head of Ushiromiya family doesn't equal the gold because the gold was borrowed. Which means that Battler can be a descendant from the first Beatrice and is legally entitled to the gold. That's why Rudolf was somehow pressed not to marry Kyrie but someone else. Together with the Ushiromiya name (which Battler got back on his return) and some proof that the gold is legally his - he skips the inheritance line and is the main target. However as long as he is oblivious to the fact, he doesn't need to be necessarily removed immediately.
5. Beato (J. or S.) came to know that some person/people from her "family" want to murder him and is trying to resolve the matter differently by letting him discover it all by himself.
6. She may be involved with other people faking deaths and all those horrors to confuse the real murderers or just to made him think.
7. Why she can't just tell him... I don't know...
I can think of a few reasons but they are just as difficult to prove as anything else here.