I ordered up trump from the dealer of the opposing team and the same person said they were going alone and asked for their partners best card. Is that legal in the euchre rules?
If the player who fixes the trump suit believes it will be to his side's advantage to play without the help of his partner's cards, the player exercises this option by declaring "alone" distinctly at the time of making the trump. This player's partner then turns his cards face down and does not participate in the play.
The player, who chooses the trump suit, either by accepting the up-card's suit as trump, or by naming a different suit, is called the maker. Before the play of the hand begins, the maker may announce; "Alone", in which case the maker's partner places his hand facedown and does not participate in the play.
Note that both these Rule compilations do not include your House Rule of a card being passed from maker's partner to the maker.