Dad has considered suicide due to delusions. Any advice?

MeDolly is speaking the truth. It gets to a point where there is no "Something" they can do.
Trying different or more medication? Keeping him comfortably sedated? It might help some but usually not when the dementia has progressed so far.
My last homecare client had LBD. She was able to remain at home with 24-hour care but had to be on several different anti-anxiety and sedation drugs. She was also a bedbound non-verbal invalid.
The staff in the memory care will keep your father safe from harming himself. It can't hurt for you to consult with different specialists to see what they suggest. Your sister is right about not setting yourself up for disappointment if there's nothing they can do.
Talk with them but don't have any expectations.
The father you knew and loved is gone. Even though he's physically still here it's okay to grieve that loss.
Maybe a dementia support group would be helpful to you. Your father's memory care may be able to recommend one.

No, there doesn't have to be "Something" when it comes to dementia, as there is no cure, no way to stop the disease, it can go on and on for years, comes to the point where one just prays that their LO passes and is put out of their misery.

Unfortunately, that is the reality of the situation.

I would see about having his medicine changed yet not build up any false hope.

Prepare yourself the worst may be yet to come, LBD is one of the worst.

Sending you hugs and support.

I would definitely pursue what you can with the university geriatric clinic and possibly a geriatric neurologist/neuropsychologist.

This is the link to the LBD association. They may have resources that are useful to you
https://www.lbda.org/

I am so sorry that both of you are going through this.

There isn't a solution to everything. But it won't hurt to ask. But realize you may be disappointed.

I believe this is what caused Robin Williams' suicide.

Yes, you may be disappointed. But asking for a second opinion, or if there is a clinical trial is almost always worthwhile.

If the geriatric specialist is not helpful, Google "clinical trial Lewy Body Dementia" and see what is available.

https://lewybodyresourcecenter.org/what-is-lbd/treatment-important-information/medications/