Few questions about how greater rift keystones work when in a party. If a party member opens for example: a grift 25 and you only have a 27 and a 37 key, does it just use the 27? i.e. pick a 25 or next keystone closest to 25?
doesn't this mean that if your party member has a bunch of 25 keys you can just use your one 27 key and essentially just upgrade it over and over again, and use just 1 key to enter the rift multiple times, while the opening party member needs to use multiple keystones?
Sorry if its a noob question still very new to this stuff.
Yes, whenever someone opens a rift it takes the lowest available key you have on your character that is the same or higher level than the level of the rift opened. Meh, sounds a bit complicated, but it's pretty easy - just like you described: your party member opens a GR25, and the game searches your stash and your character for a GR25 key, if it can't find that a GR25 key, GR27, and so on. Btw, this only works for trials; for example, sometimes you see streamers trying to get "10 keys of GR60 or higher", and all but one put their trial keys away. One person opens the trial and the others pay with GR55 keys or whatever they don't need anymore, and repeat this as long as all their "lower keys" are upgraded to GR60.
Basically, the mechanic you describe is used in the new "rift it forward" for lower GRs (speed rifts): only one person needs the GR35 keys (usually the monk/crusader because they can wear most XP gear and are thus considered to be "leecher". The other three people in group just take one random key, for example some GR40 key, and use it over and over again - usually you finish the GR35 in 3 minutes, get a GR45 key, the monk opens another GR35 key and the other three people pay with their GR45 key they got from the last run.
This is by the way a good way to get solo keys, if you have a quick group that can consistently finish GRs in less than 3-4 minutes ;-)