First of all, ?νικήσατ’ is second person plural (epsilon has been elided, not omicron).τάδε ὅπλα means “these arms,” not "these hoplites."μάχῃ is in the dative case because it is local, expressing where the subject conquered the enemy. Also notice the change in tense in the apodosis from the aorist to the imperfect in ?ποιεῖσθε, which indicates that the first verb is past unreal while the second is present unreal, and like Swth\r said, “ws” indicates cause here, not purpose. Hence, the best literal translation would be something like the following: "If these arms had not been sent into that island at any rate, neither would you have conquered those harming those enemies harming the land in battle nor would you now be making sacrifices for yourself, seeing as you have been saved.
As concerns your second question, ποιῶμεν does take a double acc. in this instance. Look at this denotation from LSJ:
do, much like π?άσσω, ο?δὲν ἂν ὧν νυνὶ πεποίηκεν ἔπ?αξεν D. 4.5; πε?ὶ ὧν π?άττει καὶ μέλλει ποιεῖν Id.8.2, cf. 18.62; ἄ?ιστα πεποίηται Il.6.56; πλείονα χ?ηστὰ πε?ὶ τὴν πόλιν Ar.Eq.811; τὰ δίκαια τοῖς ε?ε?γέταις D.20.12; ἅμα ἔπος τε καὶ ἔ?γον ?ποίεε Hdt.3.134 fin.; ποιέειν Σπα?τιητικά act like a Spartan, Id.5.40; οὗτος τί ποιεῖς; A. Supp.911, etc.; τὸ π?οσταχθὲν π. S.Ph.1010; π. τὴν μουσικήν practise it, Pl.Phd.60e, etc.; πᾶν or πάντα π., v. πᾶς D. 111.2, etc.: Math., ὅπε? ἔδει ποιῆσαι, = Q.E.F., Euc.1.1, etc.
c. dupl. acc., do something to another, κακά or ἀγαθὰ ποιεῖν τινα, first in Hdt.3.75, al.; ἀγαθόν, κακὸν π. τινά, Isoc.16.50, etc.; μεγάλα τὴν πόλιν ἀγαθά Din.1.17; also εὖ ποιεῖν τὸν εὖ ποιοῦντα X.Mem.2.3.8; τὴν ?κείνου (sc. χώ?αν） κακῶς π. D.1.18; in LXX with Prep., π. κακὸν μετά τινων Ge. 26.29; ταῦτα τοῦτον ?ποίησα Hdt.1.115; κο?κ οἶδ’ ὅ τι χ?ῆμά με ποιεῖς Ar.V.697, cf. Nu.259; also of things, ἀ?γ??ιον τω?τὸ τοῦτο ?ποίεε he did this same thing with silver, Hdt.4.166: less freq. c. dat. pers., τῷ τεθνεῶτι μηδὲν τῶν νομιζομένων π. Is.4.19; ἵππῳ τἀναντία X.Eq.9.12 codd., cf. Ar.Nu.388, D.29.37: c. dat. rei, τί ποιήσωμεν κιβωτῷ; LXX 1 Ki.5.8:—in Med., φίλα ποιέεσθαί τισι Hdt.2.152,5.37.
Again τά ὅπλα means “the arms” and is the object of the participle, not the subject. remember that ποιῶμεν is a deliberative subjunctive, not future indicative.
