There is a 10% chance my wife might allow me to have a threesome in April but I've been warned (on reddit) MULTIPLE TIMES that a threesome ALWAYS kills a relationship

Bullshit.

The change is lack of exclusivity. That can change things.

The threesome itself, in my experience, makes zero difference to the relationship. Although in my case the relationships are Multiple Long Term Relationships where a non-regular is brought into the equation. Tonnes of fun, and makes no difference at all. But this is the non-exclusive-already case.

which is why I plan to do the threesome without her

If she knows about it, I am guessing that this is exactly the same as doing a threesome WITH her.

I have 2 female online friends from her country that said "maybe" to having a threesome with me and my wife

Not sure how experienced you are with women, but there is a huge gap between two girls saying "sure, maybe" and it actually working out.

I will probably invite them BOTH to a hotel (expecting to meet my wife) then tell them that my wife had LMR to the threesome and that this was a "last minute" change in plans --- will the girls be dumb enough to believe this?

This is a fucking terrible plan.

If there is one thing that will freak women out, it is "oh by the way the woman won't be here, it's just me, the man, let's go". Doesn't matter if they believe it, they'll hate it and freak and want to get the fuck out of there.

I fully expect that if they ACTUALLY show up to my hotel expecting a threesome with my wife, then they will probably arrive horny and be expecting a threesome and hopefully will use their hamster to rationalize themselves into compliance? (if BOTH girls don't agree to the threesome then I'll just send the uglier girl home and have solo sex with the prettier one)

This is not how women work.

Relaxation and safety are much bigger drives for women than sex.

Don't expect to meet and go straight to bed unless you really know what you're doing and are super good with making women feel both sexy and comfortable. From the way you talk, this is not you right now.

Meet this women one on one to start with. For coffee. Touch them a little, make them feel sexy and special, and then bail after an hour.

Straight from meeting to sex just isn't gonna work.

Lastly -- I've been told "all girls are secretly bisexual" and it's fine/normal/expect to make the girls engage in lesbian stuff but if I feel shameful/guilty about making the two girls do that

Most girls are into this, they'll do it if they are and they won't if they're not.

In conclusion:

• Don't lie to people, they hate it.
• Things won't move as quickly as you want them to - women need some time to be comfortable
• If your wife knows about this, she might as well be involved. She might like it.
• If your wife doesn't know, then it won't change much except you'll always miss the fun times and she isn't part of that
• If you are not the sort of man who can seduce a woman by yourself then adding your wife or lying about circumstances won't help