On a category of chains of modules whose endomorphism rings have at most $2n$ maximal ideals

We describe the endomorphism rings in an additive category whose objects are right $R$-modules $M$ with a fixed chain of submodules $0=M^{(0)}\le M^{(1)}\le M^{(2)}\le \cdots \le M^{(n)}=M$ and the behaviour of these objects as far as their direct sums are concerned.