Yes, the plan is that you'll be able to marry your real-life pals in-game.
Player-to-player marriage is still now being looked into. Friends will live in cabins on the player's farm, and while the player controls when their farmhands sleep and other crucial decisions, how they live the rest of their lives is up to them.
Adding friends will involve having Robin build farmhand cabins on your land.
"Farmhands can do nearly anything the main player can do", the post explains. They can farm, mine, fish, forage, marry NPCs and take part in festivals.
Stardew Valley multiplayer update to arrive in early 2018 for PC; console launch later
You won't need to set up a server to run multiplayer. The marriage between players has not yet been sussed out yet, but they do know that it won't use the mermaid pendant.
Speaking of marriage, what's most exciting about the mode is the ability to marry other players. Each individual character on the farm will have their own inventory, but when a farmhand isn't online their inventory can be accessed through a special chest in their cabin. The invite mechanism for non-Steam versions is TBD, but likely to be similar in most cases. There will be a beta test on Steam (planned for the end of 2017), with a view to releasing as patch 1.3 in early 2018.
Chucklefish stressed that there won't be local multiplayer or split-screen (drat!), or PVP, at least not initially.
"Effort so far has been focused on overcoming the biggest technical hurdle: synchronising multiple games over the internet", Chucklefish concluded. The post said that "15,000 lines of code have been rewritten", and nearly every source file had to be changed in some way to facilitate the multiplayer addition.
The will be released for consoles as well, but the studio warned that it "will be a bigger patch than usual", and so will take awhile to get to each platform. Retrofitting multiplayer into a game that didn't have it originally is notoriously hard.