Its not an odd question, and is right on topic for this group. Where does the image come from? Are the attributions to the three deities based on attributes (lyre for Apollo, etc) or on what some antiquarian said in the 18th century and never was questioned since? I sk because its possible, in the latter case, that academic opinion has moved on and that the temples being referred to do exist but with other names. Something to watch out for. Specifically, Portumnus was the deity of ports and shores, so might have been assumed as one of the deities but it could in fact have been a different one (see note about Neptune dedication below).

Various statues of deities are in the Ostia museum and there are also photos of inscriptions from Ostia and Portus.

There are two good maps of Ostia in Gaston Boissier Promenades Archéologiques (Paris, 1895), pp. 273-310 which is, happily online. The test is in French but that should not prevent you reading the maps.

The historical development of Ostia, again with maps (and again in French), is discussed in Julien Fourniol Le complexe portuaire d'Ostie (PhD thesis, Sorbonne, Paris, 1998). Its fully referenced so could help with a bibliography.

You might also find Thomas Ashby RECENT DISCOVERIES AT OSTIA Journal of Roman Studies 2 (1912), pp.153-194 to be useful. Its in English.

There is a complete Topographical dictionary of Ostia with links to photos and plans of each building. The buildings have Italian names, so look for tempio (plural tempietti) when searching for temples. I spotted Tempio dell'Ara Rotonda, the Tempietto repubblicano with dedication to Neptuno | Castori | Polluci | L(ucius) Catius | Celer | pr(aefectus) urb(i), the Tempio d'Ercole (with photos of an altar dedicated to DEO INVICTO HERCVLEI and another to Aquae Salviae | Hercli Sacr, also the last photo has a representation of three people, is that the image you are referring to?), the guild temple and mithraeum and the Quattro Tempietti (four temples, one dedicated to Venus, and likely owned by Lucius Apuleius (thus, another might be dedicated to Isis; although Ashby suggests Venus, Fortune, Ceres and Spes)). Another temple has variously been attributed to Annona, Ceres, Serapis, and Vulcanus in other words they don't know.

There is also a color coded map of the districts of Ostia which will help you relating these various temples together.

All these goodies are linked from the Ostia Antika website.

Apart from that site, there are photos of Ostia and some more photos

Aha! And finally, the temple of Portunus plus a plan of it (both linked from here. Based on the plan, you might be able to relate it to one of the other temples from the Ostia Antika site. However, I don't even know that this particular temple of Portunus is in Ostia.

Having sort of answered your question, or at least helped, I can get all excited about this. No clear idea what it means except Epona and Ostia are in the same sentence and something about a bronze statue...

Steinzeitliche Funde, die römische Wasserleitung in einer Tiefe von vier Meter unter dem Dorf, eine römische Bronzemünze (im Jahre 309 n. Chr. in Ostia geprägt) und eine bronzene Epona-Statue sind stumme Zeugen einer über Jahrhunderte kontinuierlichen Besiedlung der Ortslage Beltheim.

Maybe related to this Imperial-type Epona relief from Ostia.