When to clean out Mom's house when she's going to AL and how to deal with eager siblings wanting her stuff?

Change the locks. Nobody gets anything unless they go to the estate sale and pay for it. Hire an estate sales professional. They do it all, clean, sort, tag, sell and take the rest to a donation center.

Is Mom self-pay at assisted living, or is she on Medicaid? If self-pay, how long will her resources last? That is, at what point (if any) might she need to apply for Medicaid.

I ask because if Medicaid is in the picture now or in the future, that will have an impact on what can/should happen to her possessions. If there is no chance that Medicaid will become involved, then you have more options.

Once we have this information we can hopefully be helpful.

Is she in assisted living now, or is that a future plan? Certainly don't start dismantling the house while she is still living there!

It seems you have more attachment to these things if you are asking this question. If she has dementia, and her move to nursing care is permanent, you don't have much practical choice but to liquidate her household. The idea of keeping her comfortable with her house staying intact is a temporary illusion that you must discard. The idea of her visiting is not practical or even necessarily possible. Your mother will forget from one minute to the next what is going on, no matter how many times you remind her. This is an horrible time for her, but her mental capacity will fade, not get better. If you don't bring up 'the house', she may not even remember it at all. If she does, she must rely on what you say. If she will never practically return to it, then there is no point in keeping up a false front or from stopping your siblings from taking things from the house. You should plan to sell it before it gets attached as an asset to pay for her care and then you have no choice.