Congrats on using points for your recent vacation.
I think that barring some amazing offers or having your other family members act as P2/P3/P4 you will not have enough Delta miles to fly Delta One (or United or American) round trip OR one way for four people, especially in summer of 2019. ONE WAY per person United's
saver rates would be 70,000; AA 57,500 in business, 85,000 in first class; most of Delta's (delta one) is 280,000 (there is an occasional 82,000 but this is rare). So to get to Europe in Delta One would cost more than a million skymiles...and that's one way! RT
can price out less/more reasonablely...I found RT to MUC (since I'm stalking these flights) for as low as 162,000 pp with a 9 hour layover on a Weds-Sat in June 2019. So I guess I'd like to urge caution in planning first/business unless it's an amazing deal (which admittedly happen --albeit rarely).
Considering a "large" group of 4-United usually has some availability, American's is pretty limited and Delta's isn't bad...at 280,000 miles one way. I just went through getting to Europe for 3 of us and that drained the AA miles I'd worked on for two years. Just a one way in Comfort+ for DM and DD is likely going to cost 250,000 skymiles.
Also, and I hate to be a Debbie Downer, often but not always, groups of saver award for more than 1 or 2 are snapped up as soon as the dates are open so if you're thinking May or June...well others have probably done that too (United has released up to 5 July, AA and DL are currently up to 29 June). I'll be staying up until midnight this weekend to see if DL will have any Economy Comfort for less than 125,000pp.
Of course, these are the Big 3 and I'm sure there could be tricks and tips from others flying from a major US city and waiting for a deal and/or flying a different or co-branded aircraft. I'm just urging caution after tearing my hair out planning for 3 people with 2 years of stored up miles and points (and a very reluctant player 2).
That depends...we flew first on AA and had old planes with no power ports and I regretted the waste of AAmiles. Maybe if you can check seatguru and assure yourself of a new-er/ish plane I'd think it could be worth it to you (or if you're like me and "what's another 7K? I like flying up front!"
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