Double-walled tubes provide significant advantages, including leak prevention, thermal insulation, corrosion resistance, and the capacity to withstand high-pressure environments. These properties make them essential in oil and gas, chemical and petrochemical, aerospace, and marine industries. One of the major challenges in manufacturing double-walled tube structures lies in handling complex geometries, particularly when they need to be bent or formed for applications like heat exchangers or steam generators. Ensuring the structural integrity of the inner/outer tubes and the spacer during forming is the fundamental challenge. In this study, double-walled tubes are manufactured using cold-drawn seamless E235 steel for both outer and inner tubes, while an additively manufactured core structure out of 316L stainless steel serves as a spacer between them. The formability of the assembled double-walled tubes was investigated experimentally and numerically using four-point bending tests. To evaluate their forming behavior, the study began by conducting tensile tests on single tubes of varying diameters under quasi-static conditions. Single tubes with different diameters and core structures were bent experimentally, and the results were used to calibrate the numerical simulations. The core structures were assembled with inner and outer tubes, and bending experiments were conducted on the assembled double-walled tubes. The experimental bending moments showed good agreement with the numerical results. The minimum bending radius was determined for different tube combinations. The results indicate that as the ratio of the outer tube radius to the core wall height increased, the minimum bending radius also increased. Next, double-walled tubes were formed using tube hydroforming techniques, followed by bending. The burst pressure was determined for each combination. One of the key effects in determining the burst pressure was the corner radius of core structures. Due to the sharper corner radius of additively manufactured (powder bed fusion) core structures compared to the nominal, the numerical results for determining the burst pressure did not agree with the experimental work. The bending of hydroformed tubes showed that hydroforming could extend the tube's resistance to failure during bending. However, using the mandrel for bending the tubes with a higher ratio of the outer tube radius to core wall height is essential since the wrinkling at the clamping area prohibits the bending. Finally, numerical simulations explored the effect of in-situ hydroforming and bending on the minimum bending radius. In-situ hydroforming enabled a bending radius up to twice as small as that achievable with conventional bending techniques. Also, increasing the internal pressure allowed for a reduction in the minimum bending radius, improving the formability of the tubes.