Hello!
Based on my own experience, I wouldn’t recommend two umbrella strollers with a connector, as this combination is not very stable nor easy to manipulate. Also, it may cause damage to the surface of the strollers, and to add to it, usually looks cheap. Nowadays, you can choose from a wide range of umbrella strollers and double strollers, so in my opinion, so there is no need for such a ‘makeshift’ solution.
If I understand correctly, the budget for the complete stroller for both children is approx. €160.
Because of the lower budget, I would consider a second-hand stroller for sure - sometimes it is worth to buy a used, but higher-quality stroller, for example, the Maclaren Twin Techno umbrella stroller, or maybe Maclaren's Twin Triumph. Both of these strollers keep their qualities even after the first round of children. 🙂
You could also consider the Inglesina Twin Swift, the Peg-Pérego Plinko Mini Twin or the Maxi-Cosi Dana For2 umbrella double strollers. A cheerful and rather practical solution offers the British Cosatto brand - look at stroller like the Supa Dupa or the Supa Dupa Go that are so much more value for their price when bought used.
It is also worth to look at a preloved Valco Snap Duo, Baby Jogger City Mini Double or Baby Jogger City Mini GT Double. They offer a relevant weight capacity and an excellent second-hand value.
If you really want a new one, I would recommend looking at the affordable Joie Aire Twin double stroller. The manufacturer indicates the weight capacity of 15 kg (33 lbs) per child, but that’s just a European standard, and I would not worry too much about the number.
Available for about €250 (new), the Koelstra Simba Twin is a little bit more expensive than you wanted, but certainly not overpriced, and even a spacious solution. From a similar price category, there is the super-compact double Britax Holiday Double - practical for a short walk, but without an adjustable backrest.