This is not possible with inbound/outbound. You can only use one outbound day, and one inbound day.

But you can choose to buy extra, normal train tickets until the border. 

You can only use 2 travel days in your country of residence so you can’t do that trip with an Interrail pass without having to pay for 2 of the trips in Germany.

If you only will do those trips it might be cheaper just to buy the single tickets.

For the trains in France you will need to buy a seat reservation even with an Interrail pass. You can avoid the reservation in France if you use regional trans that don’t require a reservation.

Highly doubt if for ONLY this a pass is worth it-but deine Hausaufgaben sollste dus ganz selber machen-bloss mal schauen auf bahn.de und/oder sncf was fix advance buchen kosten wird.

You canNOT go in any reasonable way by FR-TER=local trains from DE border/Strasbourg to Brdx.

Metz is also reachable from Saarbr with cheap local tickets, Pass SaarLorLux.