Having now confirmed that this is from the Dnghu Association 2007 update of Pokorny's Indogermanisches Etymologisches Wörterbuch, it appears the relevant passage you're talking about is on page 2651 which says the following under its heading for the pronoun se- "reflexive pronoun" (text in square brackets my own translation):
- other Zugehörigkeits- and Verwandtschaftsbezeichnungen [affiliation- & relationship-terms] (compare under eigenen
Schlagworten [its derivations] *su̯elio[n]-, su̯esor-, su̯ek̂uro-s, suek̂rū-) are:
Maybe Alb. (*su̯elio vëlla “brother (*brother-in-law, sister’s husband)”[sic]
O.Ice. sveinn “Bursche, herdsman, shepherd”, O.S. swēn ‘schweinehirt”
(Bedeutungsanschluß an swīn ‘swine”), O.E. swün ‘schweinehirt, herdsman, shepherd”,
poet. “man, warrior”; Lith. sváinis (*su̯oinio̯ s) “of Weibes sister’s husband “, sváinė “die
sister the wife, woman”, Ltv. svainis “brother the wife, woman”; O.H.G. (ge)swīo “brother-inlaw,
sister’s husband “, M.H.G. geswīe m. f. “brother-in-law, Schwägerin”, O.Ice. sveit f.
and on page 2992 under the heading for su̯ekrū- "mother-in-law or father-in-law"
lengthened grade: O.Ind. śvüśura- “zum father-in-law gehörig”, O.H.G. swāgur
(*su̯ēkurós) “brother-in-law (*son of Schwiegervaters)”, also “father-in-law, son-in-law”.
It is not suggesting that the Germanic words you cite are derived from Old High German gi-swio or geswīe. The Old High German (ge)swīo and Middle High German geswīe are given as examples of words derived from the same root used for a similar meaning (i.e. relatives, especially in-laws).
"Ge-" is a common Germanic prefix likely cognate with Latin con-, and not part of the root, which is *s(u̯)e here. The particular modern words you provide in the OP are certainly derived from the extension *su̯ēkurós, rather than from any form with this prefix. This form bares no resemblance at all to Aramaic (a)gīsā.
There is no plausible resemblance in the earliest stages of these words, or a plausible route for a borrowing at such an early stage.
It is a coincidence, and not an especially close one at that.